What year mustang is it out of? If it's newer than a fox body, it's probably going to be a few inches wider than your current rear. You may be able to run the dif in the center, but you'll go through U-joints like crazy, because the rear dif and the trans won't line up. If you keep the rear off set like your stock rear, and don't shorten one side, you'll have one tire that sticks out further by 1 5/8 in, which could cause tire fitment issues, and would look ridiculous.
To answer your question though, the guts should all be the same between the mustang and ranger 8.8. It's just the dfferences in the housings that might give you headaches.