Master Cylinder Leaking

No it was a big bolt 7.25 from the same Dart the front discs came from. I bought Dr. Diff axles to replace the small bolt on the 8.75.

So you have 10" x 2-1/2" brakes on the rear now, same exact parts as before on a different rear you were using?
Just trying to be clear...
you were using a large bolt 7-1/4
swapped the brakes from the 7-1/4 to an 8-3/4
made no other changes to the brake system
pedal effort increased and stopping power decreased

Sounds like something maybe didnt fit back together right...
were the tops of the brake shoes fully seated against the top pin before being adjusted?