I've got a '77 31' International with disc brakes. When I bought the rig, the p/o recommended that I change the vac/hyd system to electric/hyd. I bought the Carlisle actuator (about $800 USD) in my town and took it with me to where the trailer was in Alberta. Once I made the deal on the trailer, the p/o (an oil field instrument tech) did the change-over in a couple of hours, while I pretended to know what he was doing. He had a work truck full of s/s tubing and fittings, etc. and was kind enough to volunteer his labor.
I've been really happy with the system. My total combined weight is almost 14,000 lbs and the trailer alone can slow the F250 diesel and A/S while descending the mountain roads around home. I just had my local shop replace the brake pads (which I had purchased from Inland) along with a bearing re-pack, and they said that the rotors and calipers were in great shape yet.
Prince George, BC