Alan you might survey the following '66-67 A-body thread for pics, if you are looking for info on how the factory did it for '67 (& 68-70 ) A-bodys with factory disc brakes.
http://forums.maxperformanceinc.com/....php?p=5284778
GM did not use a true "Proportioning valve" on its disc brake A-body's until the '71 models. Before the '71 models, a brass distribution block (same as used w front drums) was mounted to the inside of the frame and on factory disc brake cars a round metering valve was mounted up off a small stamped steel bracket which mounted under the master. The true proportioning valve arrived for '71 models. It was a longer cast iron piece made by either Delco Morraine or Bendix, depending on the application, and mounted off the inside of the frame.
There have been many aftermarket suppliers out there for the last 20 years offering varying qualities of front disc brake "conversions" utilizing an aftermarket brass proportioning valve which mounts via a thin stamped steel bracket straight inline under the disc brake master cylinder. This streamlined positioning was basically copied from at least one used parts vendor who was using a late 70's stamped steel proportion valve bracket (originally sourced from a late '70's 4 wheel disc Seville) to mount a common cast iron '71+ proportioning valve so the proportioning valve would mount up away from clearance issues with aftermarket headers.