I think alot of the disparity in the quarter mile numbers come down to two things. #1 the particular motor, most off the assembly line weren't within 1 point of advertised compression, the set of heads,(valve job and port alinement. The cams installed centerline. The distributor setup.
The stars could aline correctly and you had a real firebreather or you could get a dog.
#2 the driver, most didn't know how to launch a car with limited traction.