Hi eh:
The original pump/motor assemblies were supplied by AC Delco division of GM. The design for the assembly changed a couple of times over the production run of 73-87. I also believe the assembly for a truck with intermittent wipers is different and not interchangeable with one for non-intermittent wipers. This auto parts store called Advance Auto Supply had two styles for my 76 truck and so I had them order both and then took my assembly to the store to compare wiring and fluid ports. One was a AC Delco and the other was aftermarket...I bought the aftermarket as it looked like the original AC Delco that came on the truck(pictures in service manual)...and was cheapest price I could find.
Regards,
Henry