i am having a hard time finding out how strong the 8.25" diff is. not sure what make, model or year it came from since it has been used in everything from the 80's and up. here are the #s i found on the casing
3723599, 10325, and on the right side has this:

 

ok i just found out that this particular one was used from 1976-1981 and most likely came from a Diplomat if this helps anyone.

 

I would think it should handle at the most around 350-400 rwhp. The 8 3/4's are well enough to handle 500 hp, and the 7 1/4's won't handle a 4 bbl dual exhaust upgrade.

 

ok thanks, i guess it is not worth my time pickin up let alone fabricating to fit the firebird.

 

Yeah, you don't want it for a custom big-hp setup.

I did test that 7 1/4 theory behind a wicked 340, though. Those granny gears sure fried that one tire for about two thousand miles. Yeah, then not so much...