going to replace the rad in my little spitty with an aluminum rad from summit racing and just checking to see if there are any issues ?

As long as it is phosphate free, I don't see a problem.

BTW, a friend is putting a tripple carb'd, cam'd, etc TR6 I6 in his Spitty as we speak...

That engine should be putting out close to 200hp...hmmmmm!!

After looking at the '99 A6Aq, I'd say G12 will do just fine in your Spitty, as that is what's in that car. Otherwise, you can get away with just about any phosphate-free antifreeze/coolant.

The TR6 motor is being pessimistically rated at ~170hp. He didn't want to get his hopes up, but either way it'll be one nice Spitty when he's done with it (being set-up as a Street Prep. or Prep. class auto-x car, can't remember which).