Unless the pump is out of a older MGA, the shaft length of the diaphragm is 2 3/8". This is true for both the standard points style pumps and the all electronic pumps. The 3" shaft is for an obsolete, high pressure, long body pump. Since Kenny says the pump was originally from a 77 MGB, I have to assume that it is a standard AUF 300/AZX 1300 pump and not the older high pressure/long body pumps (those pumps haven't been produced since some time in the late 50s or early 60s).