Unported head quickness?

73 Duster full interior street car weight is around 3200lbs. .030 over 440 with stock 906 heads 2.08/1.74 valves. schumacher headers, 800 holley, .528 MP cam. compression is probably 10:1. Best run was a 12.3 @ 109 that was with the MP.484 cam. I recently found out the throttle was not opening all the way so I'm guessing there is still more left, since I fixed it the car acts and drives completely different. Best run with .528 cam has been 12.6 @ 106 need to run it again since I fixed the throttle.