I'm curious if you can use an 82 FB gas tank on a fuel injected engine?

Do they still have a fuel return line?

 

Depends on the engine you plan to run... The FC's fuel system still runs a return, and in order to make the FB tank work with FI you either need to take the fuel slosh cup and mounting ring from a FC tank and weld to into your FB tank, or run a external surge tank setup.
Personally for simplicity and noise I went with the FC intank style pump, you can't hear it and it works just like a stock cars setup would...

Oh btw, the reason I asked which engine is because many more modern cars, such as the Rx-8 have a returnless system, so it really depends on what you are going for...

 

Its a N/A 13B from an '86 S4. Hmm... so should I probably try and hunt down a GSL-SE tank? I'd rather not weld in a gas tank...

 

Yes, if you don't want to weld then a GSL-SE tank and its external pump assembly will work just fine.