When I replaced the clutch in my 50 a couple of years ago, I had a heck of a time getting it to release. I had cleaned the splines on the tranny well and made sure sure the disc slid easily on it, but no matter how I adjusted the free play it would still hang up and not shift or go into gear without grinding. I finally set the e-brake and kept starting it with the tranny in gear and clutch depressed, then slowly let out the clutch. It finally "broke free". The disc must have been a little cocked on the shaft or something, but it's been fine ever since.

Bob