The Moroso slide rule shows 500hp/3200bs as 10.50@126.5.
7% loss is 465hp, which shows 10.71@123.6.
10% loss is 450hp, which shows 10.81@122.2.

If it really weighs 3200, and won't go at least 122 at a NJ track in the spring/fall...... Either there is something really wrong with the set-up, or the dyno numbers are happy(or a little of both).

My friends Stocker shows 530hp on the Moroso slide rule(in good air), and the motor is under 500hp. In some really good air it'll show 540hp. In the middle of the summer it'll show 490hp(east coast tracks).
At the Vegas nhra fall race in 2015 it showed 460hp.

The quality of the air you run in makes a big difference.