I've got a hold of a 454 rat motor and im looking to rebuild it and i want to shoot for 500hp. I have an eldebrock performer rpm intake for it and roller rockers. The compression ratio will be around 10:1 for pump gas. I have the good rectangle port heads for it. I will put a 850 double pumper on it and headers. The only thing really would be cam selection. No roller cams. I would like to run a hydraulic for the street but I could live with a solid cam If i have to to get to the 500hp mark.

I don't think this is still on Edelbrock's web site, but if your heads have the 2.19/1.88" valves, and you add Edelbrock's RPM cam, which is hydraulic, non-roller, you'll see 530 HP and similar torque, it'll get to 6500 rpm in first gear assuming good connecting rods, rod bolts and valvesprings. Gear it for 115 mph at 6000 rpm for the 1/4 mile drags. 120-125 if you're gonna add nitrous.
Questionable fit aside, Hooker's 1 7/8" headers will be perfect. With nitrous, 2" would be better, but woul be custom unless you can find an old set of Hedman Husslers, which were offered in both 1 3/4" and 2", your choice, but are no longer listed in their catalog.