8 3/4 Rear end for Dart questions...

If it's 55" flange to flange, actually 54 15/16", it's a 68-70 B Body rear. The perches should be 44" c to c. A body rear has perches at 43", you can actually stretch the springs to install a b rear the 1/2" on each side. Best way, no, has been done a lot over the years.

175 is decent value if the drums/pumpkin are good. If you can get it for less, even better.

Sorry that 8.75 info page is not very good.