For motor swaps,an old Massey Harris is king! Rear transaxle means you can stuff in just about anything that fits between the frame rails. You could have a nice V8 tractor that makes 100 hp on woodgas EASY!
My ATC GT30 has the same arrangement having a Clark transaxle out back. The F140 under the hood would struggle to make much over 20 hp on woodgas, but it would be a cinch to plop a V8 in there