Could anyone post a pic of the location of a 66 prop valve? Thanks for any response

What kind of brakes does your car have?

Front disc , rear drum. Thought of that after posting, knew that would be the first Question.

Dave originally 66 chevelle's didn't come with disc brakes so their is no correct location for that valve. I do believe they used a similar distribution block mounted to the inner frame rail next to the steering column. Do you already have the valve if so depending on its design will determining where it could be located. On a 67 it would be mounted on a bracket under the master cylinder.

Did the 66 Chevelles have a single pot m/c like the Novas? Were disc brakes an option?

Yes the 66 did have the single pot m/c as the Nova's. And disc brakes did not become an option until 67.