2852905 8-1/4" into my Dart??? HELP!!

I recently got ahold of a 2852905 casting 8-1/4" rear end. It is complete with a 3:21 gear ratio, and is exactly what I want for the Dart.

Unfortunately I didn't measure correctly, and took the guys word that it was for an A-Body. (He owned a Satellite, and must not have known.)

Based on what I have found, it is for a '69-'70 B-Body. The spring perches are ~47" on-center. (Didn't think they put these rears in cars that old.)

If I relocate the perches, will this rear end work in my car? I have read of people using B-Body 8-3/4" rear ends, but never this rear.

Please help! I told my Dad that this rear end would finally work, and I hope I don't have to tell him it won't. (Luckily I didn't lose any money, I traded a bare C-Body 8-3/4" housing for it.)