The belt drive pump for the 6.2/6.5 Detroit GM diesel is still available through most parts houses. That pump was used only for the turbo wastegate, the diesel trucks all had Hydro boost brakes. I would probably use an electric vac pump for simplicity, you may not need a reservoir due to the diaphragm and control valve not wasting vacuum.

1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy