Rochester has a ported vacuum port hooked to vacuum advance.. The distributor moves (advances) as throttle is opened

Truck has good vacuum at idle .. Approx 21 inches and rock steady at 500-600 rpm


Old Truck addict
1950 chevy 1 ton napco
1956 gmc 1 ton dually napco
1954 chevy 3/4 ton napco
1957 gmc civil defense napco panel