The big GMs of that era had a vacuum pump built into the fuel pump so the cam eccentric was doing double duty. If the vacuum side failed you could do a "limp-home" by plumbing the wipers into engine vacuum. We often got trade-in's at the Buick dealer with that kluge and we'd have to do a fuel pump to get everything back to as-built status. My foggy old memory thinks that you could buy a rebuild kit with diaphragms and one-way valves.

Kind of off topic but maybe interesting to a few.

Dan