IMO that's a real generous virtual dyno, the numbers are plenty high.... I've had similar sbf's with better heads and a roller cam, the "real" dyno numbers were around 430hp and 460 torque.... 503 & 464 would be great, but I think the simulator is a bit on the high side....

1 5/8" headers would be better, and tri-y's would be better yet. The tri-y's on the dyno always seemed to bring a bit more bottom end to the party.... Timing is probably about right for street and cheap gas. On track days and 100 octane, you could bump it a couple degrees.... With the 5 speed and 3.54's must be a long winded thing on the straightaways!!!!