Doesn't take much to make 425-450 with a 408, either. Stock magnum heads with a decent valve job/bowl blend, performer RPM airgap, 750 carb with 1" spacer, 1 5/8" headers, and a comp cams XE284H (maybe even XE274H), 3.91 rear would get you there and keep a decent idle.
Don't really need forged...