Based on one of my old cars, a lighter 3400 Scamp, mild 440, same converter as you, 3.91 gears. Ran 13.4@104 on 225/14 street tyres.
I reckon 13.8.

69 Dart GTS 440 mopar .590 cam, Edelbrock heads, 3200#
best et 6.45, 106.78, 10.14, 132.88 mph, 1.47 60ft
best 60ft 1.36