When I was a kid, my best buddy"s Dad had a homemade tractor that started out as a 40"s IHC truck, at least 1.5 tons. It had been extremely shortened, with 2 transmissions and almost no driveline. The rear end had duals with chains always on. But the best part of this tractor was the huge concrete block that had been cast around the rear frame area. It had lots of traction and with the IHC flathead 6, lots of power.
With no rear suspension, it rode very roughly, but we drove it all over their property. Usually the rear transmission was in a low gear, for slow speeds, but in high gear, the tractor would go WAY faster than was even half safe!!!
The homemade IHC tractor would not turn very sharp, and I suspect that it used more gas to do a given job than a real tractor would have. I do not think it really had a governor, which would have made it easier to use doing field work. But it plowed and disked just fine and I doubt that they had much money invested in it.
If I was going to build a homemade tractor, I would try to find a fullsized or larger truck to base it on. I would use a regular 4 speed truck transmission, so I could use a PTO to run a hydraulic pump. The rear trans could be just about any truck 4 speed. Power steering would make the beast a bit easier to handle.
Another possibility would be to use a fullsized 4x4 chassis with a strong transfer case to get a low range. But using 4x4 really increases the mechanical complexity.
It would be pretty easy to rig a second master cylinder to get steering brakes. With a hydraulic system, it would not be that tough to build a 3 point hitch system.
I think I would stick with a carbuerated fuel system, since all the fuel injection stuff might have troubles from the dust and exposure of tractor duty.
I think I would leave the front fenders on and maybe would leave the windshield and part of the cab for weather protection. Maybe weld up a roll bar.
Sounds like fun! Maybe I will fool around with some of my old junk that way.