I'm not convinced splitting the tractor will help and it sure adds complexity. At most, maybe loosen a few bellhousing bolts at a time to see if one was jamming something.
In-frame additional investigation might solve the mystery - such as pulling the rod caps and pushing each piston up a little to confirm this is a stuck rings problem. Then if the crank won't rotate the slightest amount with the rods loose or detached, and you have checked inside the front cover, it's time for a specialist. The crank slides out the back of the block on most of these so I think working with that is getting into specialist territory.