the mx-3 flywheels are 16lbs, the normal 2.5L flywheel is 22-24lbs. and it fits just fine.
a freind of mine put a 6lbs flywheel on his V6, he said it was a night and day differance in performance. He may almost be right... he only has that flywheel,act clutch,and spacers. He almost rus neck and neck with my other buddies v6 with FPR,CAI,Catback,and test-pipe. so that isn't bad for having no real performance mods.