[mockingbird812]

O.K. I'll bite off and give someone a target. My guess is it was a learning process. In '70 the 454 motors (LS5 and 6) had a mandatory mating with the rockcrusher. Probably took them awhile to see that the 20 and 21 were not up to the task hooked up to all of that torque. Probably saw more and more warranty replacements/reworks and got smart in 1970.