The clutch on my 73 stuck this summer. It hadn't been all that long since I had run it, but it was stuck pretty tight. To get it loose, I finally had to unbolt the engine and slide it forward to get a little working space. After I got it pried loose, everything cleaned up OK. Since the fiber disk wasn't torn or otherwise obviously damaged, I just put it back in. It seems to be fine.
Now I try to more careful to leave it with the brakes locked (which holds the clutch disengaged).