Were the brake distribution blocks in 67 the same between a drum and disc brake car, as long as both had dual resevoir master cylinders?
Or, is the "valving" different between the two blocks due to the disc brake calipers vs drums up front?
AFAIK, drum brakes used a distribution block and disc brakes use a proportioning valve. If they do in fact use the same distribution block, then there should be a proportioning valve of some sort on the rear line. My 0.02