I have a '76 Corvette master cylinder in my '48 3800. The bore is 1 1/8". It is designed for 4 wheel disc brakes but works great with the manual 4 wheel drum brake set up on my 1 ton. The push rod hole on the master cylinder is deep so it accommodates the push rod assembly. The residual valve presented a problem with very hard brake pedal and poor stopping. I removed the residual valve and the brakes work fine. The bracket assembly and extended push rod were purchased from ECI in Connecticut.This enables you to continue to use your original brake pedal set up. This set up has been in the truck for 6 years with very good stopping.