The 9" is your best option if you plan to have any kind of horse power, the 8 3/4 is a good rear end but won't handle big horse power, that is why Mopar used Dana's in the Hemi and 440 6pack cars. You could get a Dana 60 out of a mid 70's Ford 3/4 ton truck and buy the correct ends but a Dana is 100 pounds heavier than a 9" and you can't easily swap out gears.
I used the 9" housing and brakes out of a 70's F-150, I just redrilled the drums to 4 1/2" bolt circle to fit my Strange axles. The Ford brakes are 11 x 2 1/2 which work great with the 73-76 A-Body disc brakes and stop on a dime.
