What heads are you using? Torque converter? Cars weight? Tire type and size?
FWIW, my Barracuda has a similar combo, 360, eddy heads, 509 cam, 3500 stall, 4.10 gear, 3250 lbs
runs 13.1 @ 105 MPH at an altitude of 5800 ft (density altitude well over 8000 ft). With that said, I think 12s...