Not sure why a 800 cfm Edelbrock carb wouldn't be more than enough for 500 hp. That carb should be fine up to about 700 hp where it probably starts to run out of fuel. You can put a fairly big needle and seat into them but at some point they'll run out of fuel.

We did have to put the larger needle and seat into the 800 cfm carb that I ran on my low deck 470 motor. That motor made about 550 hp on the engine dyno and 475 hp at the rear wheels on the chassis dyno. Without the larger needle and seat it would run a little lean at WOT.

Those carbs work great on a 500 hp street driver. The metering rod design lets you quickly dial in the fuel curve which is a nice feature. They do have a couple of weak points but overall they work just fine on an engine like that.