If your car isn't under 3000 lbs the PG won't help it. You'd be better off with a low gear 904. You have to be right on with the converter when using a PG because that is what it will launch on rather than gear multiplication.
He has a Big Block so a 904 wont work.
Topbrent is correct you will need 4.30 or a 4.56 gear but also what tire will you run you must dyno your motor to have all the specs and car specs also for the converter shop UCC (Lenny) or PTC (Kenny) will get you hooked up so your converter will lock up.