Disappointed in my 383 on the Dyno

Granted, my ‘69 ‘cuda was an automatic but some years ago I went a 12.64 at the Mopar Nationals with the following set up.
.020 over 440 with pocket ported 906 heads, stock valves, cast iron intake, ‘68 AVS 440 carb, 284/484 Mopar cam, stock distributor, 2” TTI headers, unknown 10” converter, 3” exhaust (overkill in my opinion), 3:55 gears and 275-60-15 T/A drag radials. I’ll post the chassis dyno sheets if I find them but the car was a ball to drive and pretty much stock.