I don't know if the upper control arms on the rearend are the same setup as a 1965 Impala, but if they are you will need to add a heavy plate on the inside of the floor pan. Many years ago i had a friend with a mild b/blk and it kept tearing the mounts loose right out of the floor pan, we wound up having to weld in a 1/4" thick plate all the way across the mounting area.
Zip.