I didn't know they even made a V-belt vacuum pump!!
Is this a standard front-mounted engine? If so, you can remove the doghouse cover inside the coach to gain access to the engine. At the very rear of the engine in the center of the valley, you'll probably find a round plug. This is where the gear-driven vacuum pump normally resides on these engines. This is the same location where a distributor would be mounted on a Chevy gas V8. GM/Detroit decided to keep the same setup for the diesel engines to run the oil pump and the vacuum pump, until they started using a serpentine belt setup and went with a belt driven vacuum pump.
Casey
1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter