If the clutch facing is stuck to the flywheel there are a few remedies for that. I have seen it all too often.
1. Start tractor in first gear, with clutch pedal pressed down, while tied to tree or against something immovable. With luck the force will separate them.
2. Start tractor in neutral and while running, jam it into first gear! Sounds awfully dangerous (don't get the revs too high!) but the sudden jolt works! I watched one of the Zimmerman's do it very successfully for me.
This advice at your own risk