As others have indicated, you can broaden your search considerably by also considering the first generation Ford 4000 (4 cylinder). But be careful, these are essentially an 8X1 (so they are built with various PTO & transmission options). Additionally, you might look into the later 3000 or 4000 (3 cylinder). These tractors can be found (also optionally) with several more modern features (4x2 transmission, independent PTO, diff lock, ?). We have a '73 4000 SU, which is essentially an 861 on steroids (4X2 trans, IPTO, power steering, diff lock, wet brakes).
I know it's not on your list, but you might also consider a Deere 2040, 2240, or something similar. We have a 2240, and I find it a great utility machine around the woods (in part because of the low, horizontal exhaust). Also, like the Ford, finding parts and support for the Deere will likely be better than some of the orphaned brands.
Good luck!