Some people are going to say to narrow the 8.75, but really, if you are planning a mild to moderate engine build the 8.25 will hold up just fine.
Once upon a time everyone thought the 8.25 was crap and the 8.75 was the only way to go. Now that 8.75s are drying up (or at least getting expensive) people have figured out that 8.25s can take the power, they just need a little love.
There is a good Mopar Action article about building up the 8.25. I have it in PDF format. PM me your email address and I will send it to you (I do not want post it here and piss off the copyright gods).
Your housing "should" have the larger carrier bearings. In '75 they went to a small diameter (inside diameter is the same). The carrier was a 27 spline unit, and there were two types: 2.45 gear set version, and everything else.
All carriers up to 1996 and older will be a drop in fit. In 1997 they changed to an improved 29 spline version that has bigger C-clips. These can be found in Dakotas and Durangos (non-5.9L vehicles).
The late model Dana Trak-loc that is factory in the late model is very affordable, even from the dealer (under $200). The catch is that you will need to order specific axles that are "A-body" but with 29 spline late model ends. It will also use the larger C-clips that are readily available from the dealer.
There is also the benefit that 94-98 Jeep Grand Cherokee rear disc brakes (11" rotors) are a near bolt-on mod for any 8.25 with a 5x4.5 bolt pattern.
Having said all that, I have just completed rebuilding my 8.25 from a stock 2.45 open unit to a 29-spline 3.55/Trak-Loc with custom axles, cover and the Jeep brakes. Thread is here:
http://www.forabodiesonly.com/mopar/showthread.php?t=153229