There's a guy in Sandy Springs who will work on Fieros. His name's Eddie, I forget the name of his place, I think its right by the intersection of Roswell Rd. and Mt. Vernon. Its a "hole-in-the-wall", he normally has his lot full of police cars he works on, but he'll work on any car if you bring it to him early enough in the morning. He'll even do performance work, he put on my kit for my Z24 brakes on my '86.
I also had decent luck with the Big10Tires right there at Roswell Rd. and Hammond Dr. They'd only do back-to-stock work though, and they wouldn't touch the sparkplugs on the V6 without tilting the engine.