What Hotrod is saying about the differential ratio is the gospel. Performance from any horsepower is going to finally lead you to what ratio you need in the third member to a large degree. I am running a 305 with a Th250c Tranny and a 4:11 rear gear, stock engine w/2bbl carb in my 64. I don't compete, but it keeps up with the traffic and with the light weight rear short stepside, it will spin the tires very easily. Also, a stallspeed with any cam that has enough lope requiring fast idle is a must to keep from having to keep both feet on the brake at a red light.

Truck Tinker