I know it is possible to buy gears like 3:73 or 4:10 and put into an A4 but will any Gm gears for f-bodies work or are there a certain type of gears that go into an A4.?

 

as far as i know (atleast are comon)

are the 2.73, 3.23, 3.42, 3.73, 4.10, 4.56 are the only ones ive heard of people using... but that doesnt really answer ur question

 

It must be a 7 5/8 set for the rear end.

 

Yup and you also need gears for either a 2 series carrier(if you started with 2.73's) or a 3 series carrier(if you started with 3.23's or 3.42's). Since yours is an A4 you wouldn't have started with 3.42's though, just pointing it out. Most places you buy from you can specify which you need.