Help identify old k boom.

Hey guys long time lurker but new poster. I just signed up for an account but I can remeber searching this forum for years when I would come across equipment I knew little about. So I purchased a small knuckle crane today to put on my truck or maybe trailer. I have been buying and selling equipment recently while I'm out of work (remodel contractor for investment group who buys foreclosures). Iv done pretty well but I have been very limited on what I can buy becuase of being able to move things. I have a few friends that have machines and they have helped but its very inconvenient for everyone and it gets expensive to kick a few bucks left and right and so on. I was hoping to grab a cheap skid steer but quickly realized what I could afford (5k) would not get me anything worth having to move stuff around. Well one day as I was redneck engineering a 10ft flatbed off my 16ft flatbed truck a truck with a knuckle boom came around the corner and im telling you it was like a slow motion movie. Sun light glistened through the boom and glared off the chromed rods and it drove right at me. He stopped and said I saw you trying to move this and figured I'd give you a hand. Now this was a newer truck and a really nice crane plus the guy was probably in his 50s so he was I'm sure very skilled at what he does. He was able to throw a chain through each corner of the bed and he just lifted this flat bed up and said "where do you want it?" I told him inside my gated area (storage yard) and I ran to open the gate and he yelled "no need jr step aside" bed went up about 15ft and over the gate. I was absolutely in love with the idea of a crane I instantly started looking for one. By the way yes I had to open the gate to get the chain off the bed lol. I think he was showing off alittle becuase I must of looked like a 15 year old kid with a crush when that crane unfolded lol. Ok sorry for the story just figured I'd give some context so I didn't get a bunch of people telling me theres alot easier ways to skin a cat. Plus I buy equipment from all over so sometimes you can't get a forklift/skidsteer/tow truck in places people have there stuff sitting around. So I ended up buying a crane the next day. I jumped in head first and im not sorry. It is mounted on a truck frame and its welded on. I wasn't sure where to put a crane on my truck (behind cab or in the back) and I was told by 2 people definitely not to mount it in the back. That's what I was leaning toward for the extra reach. Plus I don't really hual super long loads like logs so I don't think boxing out the bed with the crane would be a big deal. But this one looks to me like it was mounted on the back of the truck? Either way, you guys tell me. But the crane is in very nice shape for the age. I was told a model number but I don't see it anywhere on the crane itself just what the seller said. I was also told its 16ft reach and 6800 max lift at the truck and 2565 at 16'6". I'll include the lifting chart he sent me. Again I don't know if this is really the model or not it's just what was provided. So my questions. Any one have any experience with these? What was this or at least this style of crane made for? How can I test/check everything on this to make sure I don't waste a ton of time and money fitting it to a truck to find out it's useless? I really appreciate anyone who takes the time to respond and share your experiences and knowledge with me. I'd love to also get some advice on safe operation. I do understand the chart as far as what to be able to lift but I have never used a real crane only small service truck cranes for very small stuff. Would I need to add down rigger straight back if I mount it in the back? It does have the 2 the come down beside it but it would have the entire weight of the truck as a counter weight right? Plus the bed is only 16ft and so is the crane so I wouldn't be able to do anything in front of the truck anyway is that the correct thinking? Also does this crane spin all the way around and if so do I lose any strength of capabilities if I do turn it 180° to work? Why is there a hollow box under it? On the information sheet the seller provided near the bottom it has an image of the crane mounted behind a cab with an arrow pointed to the back and it says "load side" does that mean that is the only way it should be used or just referring to it becuase thats how it is in the picture? Is that picture even the right/same crane? Sorry for the probably dumb questions but I did not grow up around this stuff. I'm very eager to learn but to do it safely. I guess I should also ask if there is anyway to find a service book or anything like that?
Thanks again guys.

A few more pictures

Anybody? Someone has to know what this crane was made for?

I don't see any aux hydraulic lines, so my first guess was wrong. It looks like a self loader for a medium dump truck, but no hoses for the grapple.

Now I know where the asians copied their small cheap truck cranes from. I had a client a bunch of year ago that was importing cranes that looked just like that into this country when the gray market was running hard. I think he brought in twenty or so units. They were meant for those cab over flat beds like the Hino and NPR rigs. The worked pretty well for what they were but there was a huge issue with the outriggers. They didn't extend out far enough and the hydraulics were too strong. My client was setting a rock in a hole for a customer when the truck tipped over on the side he was operating from. The only thing that saved his life was that he fell in the hole where the rock was supposed to go. Basically as the rock came down it set on the other side of the hole and didn't roll on top of my client. When you install the thing, you had better figure out those tipping weights before you start using it.

Looks pretty clean for an older unit. Kind of an odd mount on that frame . Im thinking you will have to restore the mount base back to as it looks in the load chart,so you can bolt it ,not weld it to your frame.Rear mount is good for shop guys working on machines ect limits you to hauling long or bulky cargo Might be weight distribution issues to depending on what truck its on.. behind the cab lets you haul long stuff but limits the reach . That crane wont swing 360 deg. so be sure you have it set so the limits of rotation work for you. Assuming you are competent at welding and fabricating have a Look at some smaller mounted cranes so you understand how the bolts are installed. Use grade 8 or 4140 bolts and fly at it.
As for running it be sure of the ground under your outriggers ,make some wood pads . With no load cell and limiting stuff this is craning by the seat of your pants. Try and know the weight of your picks and be aware of the load chart and reach . Breaking from those parameters means breaking or tipping the rig or at the very least abusing it. The example you gave of setting the flatdeck over the fence might the type of lift to avoid until you know your machine. Dont pick something heavy in close hoist it aloft and think you can reach over holes ect. where you can, float the heavy ones close to the ground if you have to tip it wont be catastrophic. Remember the crane will probably have a structural capacity in the closer ranges and a tipping capacity further out . The weight of the truck and the deck will also contribute to the cranes tipping capacity. Check this when your rigged up with a test weight at 10% over the chart weight and swing thru your working radius low to the ground and see how it performs. All this said if your going to work with a crane rules and regs ,certification come into play, its unlikly this crane would make the grade in that world.

Thanks guys and I will do as advised with some lift ans range testing before just putting it to work. I am not going to be a daily crane user but will still like to know its limits. I did see a few things online that lead me to think log grapple as well but like you said there's no lines near the end for s grapple and no extra controls either. I'm starting to think about making a trailer out if the frame its already on and just doing a pony motor setup. Would anyone know what kind of pump would be good. Psi and gpm parameters for something like this? And then what size motor for whatever the pump ends up being? Thanks again for the advice

You could check the existing hoses to see what their max pressure is listed as. That's just a start, because who knows what maintenance has been on this machine.
Assuming the load chart above is for this crane, you can take a bunch of measurements (radius, cylinder mounting locations, cylinder diameter, etc) a bit of trig, and get yourself a rough psi required to achieve the rated lift.
It's naturally also possible you might find pump requirements based on the model number by calling Prentice...
I expect you're not going to need a lot of GPM for this. You don't want it running all that fast anyway since you're not going to be worried about cycle times. I know I'm barely cracking valves on my crane so it runs slowly. Once I get a better feel for it, and have all the maintenance done the pace will pick up, but then mine is setup for clamming, so speed was a consideration in the original design....
I imagine a unit like yours would be incredibly handy. Mounting to a trailer might work, but I expect you'd loose capacity since you don't get all the weight of the truck to help keep it upright. That would also be hell on the trailer design in terms of tongue weight.

The hollow box was likely just to protect the supply and return lines on the bottom of the hydraulic tank.

It originally wasn't welded to those frame rails, you can see the holes where its supposed to be u-bolted down to the frame rails of the truck.

If you mount it on the rear of the truck, the non 360 rotation is going to be a pain, you'll have to pay attention to which way you swing around all the time. You may think it won't be a pain, but it will.

A chain fall hanging from the hook or shackle on the boom, is really nice if you have to set something straight up and down, without moving in and out.

It looks like they had the crane set up to be lifted/drug onto a roll off dumpster truck, and then pinned/ chained it to the bed. The sub frame has a hook on it and is about the right length. They probably had a set of quick coupled hoses or a pony motor to drive it. The box was to keep from ramming the lines off when they laid it off.