Fresh 727 Street Strip Trans S.B. Wont Drive

The pump itself should not have been a problem with the converter fitting. Spline counts on the pumps are all the same on all years. The only differences in pumps is the early pumps used a 1/2" wide stator bushing and newer ones used a 1" wide bushing and the vent is different. You cannot mix early style pumps with late front clutch carriers because of the difference in the bushing and the oil ports aren't the same/won't line up.

What year was the old pump? What year is the new trans? Did you count the splines on the input shaft? Did you change the rear clutch pack that has the input shaft pressed in it?