That seems in the ballpark. You'll just have to try it and then go from there. I had a bunch of 475 rwhp pulls with that low deck 470 motor on the chassis dyno but that was about the limit.

Better head porting and more intake rocker ratio would have been the next items for me to try. If you're shooting for 500 rwhp you'll probably need to thrash the combination a bit. I'd suggest 1.6 or 1.7 rocker arms on the intake and 1.5 on the exhaust as one area to test.

Have the heads been modified? The CNC porting from Modern is a pretty good package. I think you'll need some good port work to hit your 500 rwhp goal.

I'd be very surprised if the 6 pack intake would support 500 rwhp, it really isn't a very good intake. Guess you'll find out. If you do back to back testing with the 6 pack vs. a Performer RPM I think you'll find some gains.