Well I unhooked it from the tractor, and tried chaining it to the tractor, and pulling with my truck at the other end. No go. Got to thinking this wasn't the smartest setup. Might rip something off the tractor before this thing comes apart.
The chains were wrapped around the shaft right against the yoke. I moved the mower over in front of a 40" oak tree, and chained one end of the shaft to the tree, and let the shaft hang down. Just about emptied the can of penetrating oil into it, and tomorrow will give it another go, with the truck pulling against the tree this time.
The truck is my 3/4 ton diesel, so if it is going to come apart, this SHOULD do it.