the only thing that is the same is the doors, glass, and drivetrain. fenders, hood, decklid, and bumpers are all different. they do make body kits for the sunfire. as far as performance parts go to www.paceparts.com
(not advertizing) all they handle are GM parts for just about any GM. i haven't been there in a while but i think they sell body kits for cavaliers and sunfires.