Welcome to the Bolt
You have Air Over Hydraulic Brakes that were added (not factory). The factory AOHB system maintained the brake pedal pushing the MC, so even if you lost air you still had brakes. Your system will have an air treadle pedal and no mechanical connection to the MC.
Full Air Brakes didn't come out of the factory until 1957.
Any modern air brake compressor can be made to fit. Since it's not factory you'll need to provide pictures and data tag info so the experts here can help you.
Was the truck EVER titled in your name, even in a different State? If it was you need to contact that State DMV and ask for a duplicate title. If it's not that easy, you'll need to contact your home State DMV for instructions on how to get a new title...every State has a process and they are all different.
Mike B
