Your going to have the engine out anyhow, on those machines its so much easier to work on once it out of the loader or dozer. When out, if I recall, maybe a dozen bolts and it comes out with the radiator, pump and clutch, but its been almost 20 years ago now since I took mine out.
Do a complete tear down of the engine, pull the crank and cam, have them both checked over at an engine shop for wear, same for the rocker assembly, pull the sleeves and pistons, basically tear it down to the block, take everything in and have them check it over for wear, it will probably need new bushings for the cam. Take the injectors and pump in a pump shop and have that gone through as well, most likely the injectors will need to be rebuilt so the spray pattern is right and the pop off is set correctly, that helps a lot with starting, the head will definitely need to be done, the more the valves wear up into the head, the lower the compression is in the engine causing a major hard starting issue. Get new sleeves and pistons and put those in, the engine shop will check for the top of the block to see if it needs to be planed or not, then put it all back together again. Have the flywheel surfaced and put new front and rear main seals in, if it were mine, more than likely I'd put in a new clutch since its handy and apart and have the ring gear checked over as well, it only ends up stopping on four spots on the ring gear, have someone heat it up and turn the ring gear just a little and when it cools you have four new wear surfaces for the starter to hit again, have the starter gone through, if it were mine have the alternator checked over as well, since its apart and handy. If it has a turbo, see if its leaking at all, if it is, find out if you can put a new cartridge in it or buy an aftermarket turbo and install that, some had them others didn't, they are a basic altitude compensating turbo, not a huge hp gainer, but the turbo helped them start better, hence deeres idea at the time to improve the starting issue they knew about but did nothing to remedy in those engines.
While the parts are away being gone over, take the fuel tank off and pressure wash it out, use a bore scope and look inside to see how badly rusted it is, if its badly rusted, either figure out how to get it cleaned out, shot blasted or whatever to clean it up, those steel fuel tanks have been a huge pain in the a@@ lately for rust issues with my own stuff, replace all the fuel lines with new rubber lines, if its got steel fuel lines on it, throw them away and put on good quality rubber lines, then put at least one cheap inline fuel filter on it before it gets to the engine, somewhere easy to replace.
Beware of a simple truth of those vintage engines deere put out, even new they were not the best starting, so I'd put a nice block heater if it has a port in the block for one you can get at, and also a tank heater before you put the engine and assembly back in so you can plug the heater in when it gets colder out, as in anything under 40 or 50 degrees it needs to be plugged in so you don't have to use either, even brand new, the bulk of those engines needed to be warmed up with a heater in order to start without either. If your comparing them to any more modern engine, your in a for a very disappointing feeling once you get it back together, all the above will help, but it will still not start like any modern diesel built today. I've been around hundreds of those engines over the years, from trenchers, to tractors, generators you name it those engine were put in everything back in the day and as one guy once told me, they need a block heater or they catch a cold every time they are left out in the cold. With putting two heat sources on the engine, a block heater as well as a tank heater, you have a second option WHEN one quits working to warm it enough to start the engine till you have time to replace the one that doesn't work, my 450 crawler loader has both on it and it too needs all the above done, but when done, it will again have two options to plug it in, if it were in a tractor, no bid deal those are easy to get at to replace, but a dozer or especially a loader, you need to raise the loader in order to get at the engine, which means it has to start to raise the loader, then another hour to find the heater and a couple more to actually replace it is the reason why I put two on my own loader. The tank heater on mine is up inside the lever compartment tucked up under the dash, up enough so its out of the way, but still able to get at if it doesn't work to replace it without having to start the engine and raise the loader up in the air, I just routed the hoses up through the impossible engine compartment to where I could still get it to work, that way the heat cord is zip tied to the hand grab handle I use to haul my fat butt up onto the tracks to climb into the seat.
The next newer vintage four banger starts a whole lot better than the vintage you have, and yes I do have both vintages of engine I still use, along with a newer version still, each newer vintage starts a lot better and with colder temps than the version it took the place of. Compression and fuel spray pattern were the two big things that helped the starting of those engines, that and having a place to plug them into when it gets cold out. Best of luck.