HP 500's came with stock Chevy rods. They are fine up to about 600hp. As for the Cam, listen to Merc, I tried the Gils on the dyno back in 2006 and it did show some signs of reversion plus they killed the hp. I have had NO problems with the CMI's, but I am in fresh water too.
You may want to rethink the blower option. You could easily get 650 with a small blower and low boost. You could also continue to run the Gil's!
BTW I run 89 pump gas!