WOW !, Sounds like you have a Wagner Air Brake Conversion, which was an accessory add on from Chevrolet Dealerships. That's a "Rare" setup, you have there. I've only seen one, in all my years of messing with these Advance/New Design '47-'54 GM trucks. I'd like to see some photos of your truck, & Air brake setup. Air brakes weren't available on Chevrolet Trucks from the Factory until around 1956.
