Alright I think I answered myself here. Unit numbers match for the truck series. The confusion comes from the understanding that the 11" diaphragm unit does not match this. This truck has the optional brake package, the 12.75" diaphragm booster style which has a third lead at the tip of the unit that feeds back to the master, "the function of which is to compensate for for any loss of fluid from the Multi-Vac hydraulic cylinder."
In layman's terms, a high pressure return line. This hydro-vac was a factory available upgrade as per my book in front of me. So, now to locate the corresponding master cylinder part number to work with this unit. Apologies for overlooking a page in my manuals and missing this.
