well the 420a is pretty good powerplant. most anybody says its junk, but you got to know what your doing. bolt ons give you some boost in power, but if you want more power sticking N/A look into a port and polish job, mild street cams, extrude hone intake(or new high flow), larger fuel injectors(or a few extra ones), aluminum flywheel, and the big one new pistons, rings, and rods(maybe even crank but your crank is good) and up the compression. but youve got most of the bolt ons that most people do.