On my '65 w/ SM420 4 spd, it's an 11" clutch. It's not all that difficult. I replaced mine earlier this year and had never done one. Took the whole day but, was up running by evening. You'll definitely want a jack if it's a 4spd. I didn't use a jack but, my buddy we affectionately call Shrek helped me. He's 6' 5" and 290 lbs. The truck was on a lift and even with his strength and size it wasn't easy gettin' that thing outta there. As you're disassembling, try to take mental pictures as your takin' stuff apart. Use a digital camera if you have to. Then reassemble in the same order.
One thing we forgot to do was drain out the old oil and that made it a bit heavier (not to mention messier) when removing. When it's back together, don't forget to adjust your pedal. You need to have an inch or so of freeplay.
Good luck,
David
