only problems are 400 sbc and 454 bbc is external balenced. all others internal balenced. then make sure its same ring gear dia as there is big and small. but small is old school you shouldnt have that. then last crank bolt pattern is diffrent from 1 peice and 2 peice rear main seal.
so yes a 305 to 350 will work if same ring gear size and same crank pattern.
and most auto stores have new hd versions for under 30 bucks. i just had to remove my tranny for a sec time as the clutch didnt work with hydro parts swaped in. and if you install used part in there and have problem again you will be kicking your self in the butt.