?? RHS or edelbrock heads for my 408 ??

IMO, Either head will need substantial port work to reach that level. With what you're planning, IMO, I'd run the RPMs with a CNC program. The porting level required will be fairly substantial and RPMs being aluminum will be easier to do, more than likely cheaper, and lighter to boot. I feel once you have to port them, the advantage and lower initial cost of the RHS heads is lessened dramatically. It might actually be cheaper to run a better head with less porting if your goal is a real 550hp.