[Bandit]

I have had a few 1987 Grand Nationals. In my opinion for an exhaust system would be to get an ATR Stainless Steel cat back 2 1/2" duals. Get the Stainless Steel ATR Pitbull mufflers too. I have had that system on 3 of my cars. I have also had a 3" ATR SS single shot exhaust which is actually louder. You really don't need 3" unless you are really going to do alot of mods. The 2 1/2" dual exhaust system is made for the Turbo Buicks. Perfect fit. Tailpipes exit behind the rear wheel like the stock system with a nice angle cut to them.
Both websites listed above are the primary two in the Turbo Buick world. GNTTYPE.org has alot of good reading. TurboBuick is an excellent message board like Yenko.net.
Hope this helps. Enjoy!