Hy mikes 63-k10, the trucks you're asking about employed three different braking systems. Vacuum over hydraulic, compressed air over hydraulic, and full air brakes. If you are going to hook up to a full air brake trailer, the easiest system on the truck would be a full air brake system. Some of the old trucks which were equipped with compressed air over hydraulic brakes, plumbed a hand valve into the compressed air system and used it to control the air brakes on an air brake equipped trailer, this would not function automatically as would be the case if the towing vehicle was equipped with full air brakes. Earlier semi trailers were equipped with vacuum brakes, and it has been decades since I've a functioning system, hope that helps.
