the 66 might have had the newer rear in it, but i had a few with the drop out in here, the internals are not the same, but the bands, clutches and bells might be there are rebuild kits for these trannys so you don't have to even think about swaping parts from one to the other type also these trannys for cores are avalible as well i have eight trannys in all on the shelf in the garage for 65 year when i looked yesterday yeah i know why just because i can i guess ; - ) Greg