turbo header size?

For a near stock LS1 how big should the primary's be? I'm trying for 500+rwhp. Would using 1 5/8" be too restrictive? 1 3/4" enough? Or bigger? This would be a twin LS1 setup. Around 6-7psi all stock motor(maybe ZO6 cam w/pushrods). I don't plan on upgrades until i rebuild the motor(long time if ever, unless I break it :p ). Then I can get bigger headers if needed. This will be a daily driver when its not snowing. I'm trying to keep costs down(going to need to beef up the drivetrain). The reason I even mention 1 5/8" is that I have shorty's already and may be able to figure a way to use them. And I saw that the ls1motorsports single kit uses a ported stock manifold w/ 2 1/4" crossover pipe. The turbo's I had in mind are turbonetic T3/T4 hybrids.

Or would a single T72 ot T76 be better? I am a turbo newb so feel free to correct me as needed. I know either way it will probly cost more than just a supercharger. But I would rather go turbo, just my personal preference.

The smaller headers are fine for what you are trying to do. A T-60 should get you the power you want if the tuning is there and the motor holds up. A T-72 should be good for 600-650rwhp and a good T-76 will support 750+. The T-44 turbos seem to max out at around 450rwhp on the Mustangs, which is a lot of power but not 500:)