I have 1967 Cougar with manual drum brakes all around. It has always stopped alright, but thought maybe I would atleast put front disc brakes on for increased stopping. I’m a purist and I have a complete front 1967 Kelsey Hayes disc brake assembies that have been on the shelf. I thought about just rebuilding those. Would I need to change the master cylinder and install another proportioning valve? Just curious on thoughts and best direction to go. I don’t want Granada, aftermarket Chevy, or some other brakes that wouldn’t have come on the car in 1967.
The factory shop manual answers all these questions. You need to get a copy. You will need different plumbing, a proportioning valve, and a different master cylinder. If you don’t have power drum brakes you will need a power booster as well. If you install a booster you will need a different brake pedal and support also.
I did a disc to drum brake conversion on my '68. It was a manual drum brake car. The “right” way to do it is as Royce suggested. However, I did mine as a manual disc/drum setup. It used the original brake pedal and a master cylinder from a mid-70s Maverick/Comet with the same disc/drum setup. I had to shorten the pushrod slightly in order for the brakes to release, but otherwise it bolted in. I used a manual aftermarket proportioning valve instead of the factory style proportioning valve. I also have a line lock installed. The original KH brakes are known for being rather leaky, so I used some aftermarket (SSBC) versions and haven’t had any trouble. The brakes take a bit of muscle to stop the car, but really not too bad. It was definitely worth the hassle.