I think the drive cone is seized to the coupling on the axle shaft (it is keyed to it but my understanding is it supposed to be driven in slightly by the adjusting nut to apply pressure to the inner face of the wheel hub, to lock it up) and its seized to the inside of the wheel hub. If my memory is working, I believe the tapered cone is bronze, so it should not be seized to the cast-iron hub or steel sleeve.
What I have seen is the steel sleeve crack and expand, preventing the cone from sliding on the sleeve.
I made a puller and was able to pull the hub along the axle 3/8" along with the coupling and drive cone along. I didn't want to go any further and make a mess or trouble, If the sleeve moved on the axle, this may be the easiest way to remove the sleeve and the cone, clean & check everything, then re-assemble. so then followed the end play adjustment process. However, hand tightening the crown nut per the manual will not draw the hub back in to the original location (If all parts are cleaned and deburred the pieces should move easily.) so I mechanically tightened it back up, backing off after. This was the only way I could drive the coupling, cone and wheel hub back to the original location. The left-hand wheel hub has two square tangs which engage a side gear in the differential. ...If it is moved outward, the tangs disengage from the gear, so care is required to re-install the hub.
Once driven back I went ever so slightly further and the rear end did seem to lock up. With some giggling I was still able to move the axle though. I essentially followed the end play adjustment from here on, but since it was taking a tool to tighten the crown nut to achieve binding I stopped at that and just put it all back together.
I pushed the tractor a bit and it was able to move around, but once in awhile it did seem to locked up and I was not able to move it with the transmission in neutral. So maybe it just needs more end play adjustment.
It also seems like there is some backlash in the worm gear, I can rock the tractor a bit before it binds up on either side, is that normal too? I have to think it is especially with something this old. Some backlash is normal, but making a lot of turns with the differential locked puts excessive stress on internal components.
I think go now end play adjustment is something I should put off until I can get the drive cone to free itself from the wheel hub and the locking pin removed from the right hub. ie: I need to be sure these mechanisms for locking up the differential are free, I agree !! otherwise I can't really tell if the differential is working or not. I want to be able to jack up the rear end and see the wheels drive in opposite directions to verify this.
Does anyone have a suggestion for freeing up the drive cone in the left rear hub? I'm worried about using PB and screwing up the seals. I don't think PB will hurt the seals, but as already said, it may be a good idea to replace the seals while everything is apart. ....If you don't want to do the seals now, cover the threads on the axle end to prevent damage to the seal while removing/reinstalling the hub.