I have a few questions about the proportion valve on my 66ss. When I bought the car, the guy who owned it had already done the conversion to disc brakes using 70 chevelle parts. I will be replacing all of the common wearing and aged parts as normal. Im not exactly sure if the proportioning valve Thats near the master cyl is the 70 component or the 66 piece. What does the 70 part look like? Or, where can I find a picture of one so that I can verify? And also, are proportioning valves common wearing items? I will replace if necessary.

Thanks again for everyones help.

Since the 66 models did not have disk brakes, we can assume that the proportioning valve must be from a 67 or newer. Drum brakes did not use that valve.

From 67-70, the proportioning valve was called a Metering Valve and it was mounted near the master cylinder on a short section of brake line. It was a small round unit about 2" x 1.5" round.
Starting in 1971 the metering valve was no longer used. The proportioning valve used in 71 and later is part of the rectangular block, usually mounted on the frame, and part of the brake system warning light switch.