Im working on a GP 63 series TX1508A direct mount hollow 1inch shaft. This model has the built in unloader and bypass. The guy is using this pump for fleet washing and frequently has the thermal relief pop on him due to running in bypass and over heating. Packing assymblies are toast but wondering if a traditional style pressure head could be put on this pump with an external unloader so it would be possible to run bypass water back to the buffer tank. Is there an interchangeable pressure head? Thanks