We had almost the same combo in the 64 Plymouth. We ran 3.91's, but felt the 60ft and ET would be better with 4.10's, but with a 28" drag radial, the rpm was over 6000 at the finish line with the 3.91's and the same converter as you (drag radials don't grow so the finish line rpm is significantly higher) With stock heads (template ported), it ran out of steam over 5500. Ran a best of 11.74 @ 114.