I am not sure how big a cam you need to hit the 500 hp mark. There are folks on here that have direct experience with that who can answer that question. There have been quite few people who have used the VVT 6.4 hemi cam with good results. If you go that direction you should be able to keep the VVT and not have to worry about locking it out. Not sure which 5.7 heads you have, but while you have the heads off a good performance valve job shouldn't set you back too far and should help you reach your goal.