The Cardone 1057577 Mike listed has a 1.75" bore which matches the one in your picture...
Is it Air Over Hydraulic Brakes (AOHB)?
Does it have Tandem Axles?
Engine size will help with part numbers as there are many different set-ups...
Also, the Hydrovac or AOHB Booster will be under the cab mounted to the side of the frame rail.
Mike B
