I am about 45minutes away in Colorado Springs...I am running 10psi safely on my 145,000mile L28ET on my ZXT and will eventually not go more than 12-14psi for reliability and for the sake of keeping the rods in the engine and not blown out on the road. At 10psi my car is pretty darn quick too.
Not trying to be an *** but:
1) you make no mention of an intercooler???
2) 20psi...??? that is a freaking lot of psi - are you for real?
3) Why didn't you get the ARP stud conversion kit instead of the bolts?
4) Can the Holley carb take that much boost with a draw through set-up.
5) You make no mention on your bottom end, forged , stock????
6) Ported intake, which intake, how is it ported???
PLUS Nitrous!!!....
Good luck...hope you don't end up making a paperweight or boat anchor out of your engine.