Yellowstar, That is great. Yes you are right about the engine and rear suspension. Funny enough that you should think that way. It is a very common upgrade today to make these old blister come alive again. As for the rear frame rails, We all have done this. My 1972 HD had this problem. We did the tear down and split the rails. I was lucky enough to find a set of housings that were in mint condition so Vic Rowlinson and I cut all the rear bolts and drove them out Then lifted the frame rails out of the chairs .Undid the cross members and all that was left sticking out was the two rails from the back of the cab to the tail frame. We then split the frame rails and removed all the rust and such. Had new frame inserts bent up and main cross members . We then installed them and started drilling. Pulled all the rear ends apart and installed them in the newer diff housings and all new seals ,Brakes and all else we figured that could be a problem. Vic repainted the back end and we were back in business. I should have gone with the upgrade Nuway or Pete -airtrac air ride suspension, This would have been the way to go. But being a purist I kept the rubber block suspension, Kind of like driving a 2X4 with steel wheels You kill two birds with one stone so to speak, Because you will never touch the back end again . Then you get into the engine department. How much power would you need/want. For the most part , The 3406B is more than enough for whatever you would want. By going this route ,you would not need to install the air to air assy, and that is a pain in the a##. You can still keep your shutters and for all intents and purpose nobody can tell that you have changed anything because it still looks like a NEEDLE NOSE HD Hayes and it rides like a mattress. There are steering changes you can do to replace the old Vickers system as well if you so decide. I went with the original 8V71 N and installed dual 9 inch Donaldson mufflers and stacks. This was a little problematic as for visibility because it does tend to give you a blind spot on the drivers side, Just something to think about if you lay out your plan to go this route. There are brushguards around, and not really hard to come up with. I saw in the pictures that the battery box cover was laying on the ground, Be sure to grab that ,if for no other reason that having a template to make a new one if needed. Also ,look around and ask him if he has the muffler guard around in the shop maybe, with the engine side panels. Sometimes these were removed because the new muffler was a 10 inch instead of an original 9 incher and the brackets would not fit anymore. All this is not a biggie because they are around and not hard to make. Trust me here The new wrap around ones with all the holes in them like the Kenworth ones don't work they look like hell and just don't look right. Stay with the original style with a grab handle,they were and are the best.. Well what else are you concerned about??? You can always PM me if it gets intense LOL