will rear end fit??

I think it will be too wide. I haven't measured one personally, but according to Hemings the 9.25's that came in the 75+ B-bodies were 57 3/4" flange to flange. That would make them about 3" wider than the 68-70 B-body 8 3/4, which is already almost 2 3/8" wider than an a-body 8 3/4. I run a 68-70 b-body 8 3/4 in my Duster and I definitely wouldn't want to go wider than that.

But I'm assuming that the 75+ 8.25 is the same width as the 9.25 for those years, and it might not be. Here's the info
https://www.hemmings.com/magazine/mus/2005/12/Chrysler-9-1-4-inch-differentials/1281744.html