I’d try opening up the lash .004-.005 and see if that impacted the 60’ time

For perspective on the stall speed....... the Normal T/A 8” Race converter for a 440 bracket race engine would flash about 5600.
That configuration was derived long before there were Indy heads.......... so it was lotsa stall....... with small heads.
Typically, the trend would be to increase the stall speed as the heads got bigger.

My take on the 8” of rear separation is........ it takes(wastes?) energy to wind the springs up that much.
If the car didn’t lift so much........ maybe it would use that energy to move forward instead.