I put a 250 in my Burb, 5 speed, 12 bolt rear out of a 68 Chev Van. I used the tubular V8 motor mount from Chevy Duty, cut in the middle to make it fit the 6. used the tubular tranny mount from same. I used a spacer between the tranny and bellhousing instead of the cutting of splines and other mods to male the 5 speed work.