Mid sized tractors run from about 45 hp to 75 hp. Typically they run on diesel. My tractor is an older Massey Ferguson 150 with a gasoline Perkins, 3 cylinder engine. I live on a lot with lots of feral pecan trees that are too close to each other that need to be thinned out. Pecan is a very energy dense form of wood. Also, many local farmers trim their trees or limbs that fall off trees, and they would be all to happy for me to haul this off for them. In fact, if I can show them how it’s done with my tractor, lots of farmers around here would be happy to convert one of their tractors to wood power in case fuel costs get too high again. A wood gassifier kit set up would need to be compact and out of the way for field and utility use. The nice thing about using a kit on a formerly gasoline powered tractor is they usually have a pto on the back that is used to power a lot of implements from rototillers, wood chippers, to generators, and much more, so a tractor conversion would be very useful for a lot of chores around the farm. Would you have plans for something that would work on tractors of mid range power abilities?
I don’t know where to find plans, but Ron Lemler has a pretty nice setup.
That is a thread of @Matt setting up a Farmall M about the same size as you are talking about @Wayne also has a international he runs on wood gas so it definitely has been done and documented on here.
Go by engine size here and not by HP… the Farm All I did was something like 240 ci. This is a big engine not a small engine like the ones I use with the same rating. Id just build a WK and tune it a bit. The tractor I did was turbo, I did not get a whole lot of time with it so I have no idea if that turbo made it or not. However, I could not tell the difference between gasoline or woodgas. Maybe due to gearing Im sure under some load might be a different story. But I was a fun project and one stepping stone to where I am today 
Link to waynes tractor project
Arvid Olsen, a DOW member here had done quite a few woodgas tractor conversions too.
Search all of these up on the Woodgas Farming sub-section. Find that under the stacked-papers icon in the top tool bar.
ArvidO’s will be under his tritowns name.
Regards
Steve unruh