OK I finally had a chance to go out into the garage and work on my brake pedal being too high. I thought I had the wrong master cylinder but the trouble turned out to be I didn't have the push rod and that little rubber keeper all the way seated in the end of the piston. See what I found when I pulled it out in pic #1.
My push rod is original to the car (1867 Barracuda) and it came with the four piston fixed caliper disks. When I went to the larger ball joint and more modern sliding calipers I used this push rod with a manual disk/drum master cylinder for a 1974 Duster. The push rod for my car is right at 6 inches long from the piston end to the center of the pivot bolt. See pic #2.
When the push rod is fully inserted into the piston, it goes in right at one inch. You can see from the mounting face of the master cylinder to the center of the pivot bolt it shows 5 and 1/8 inches. If you add the space between the mounting face of the master cylinder and the end of the piston (where the snap ring retainer is) you can see it easily subtracts an 8th of an inch from my 5 and 1/8 measurement therefore giving me a full inch of depth to the piston recess. See pic #3.
The blue tape marks the depth of the insertion from the mounting face of the master cylinder. See pic #4.
With the push rod fully inserted into the master cylinder my brake pedal is where it is supposed to be in the resting position, even with clutch pedal. I thought this was going to be a exercise in "musical master cylinders" but when I realized I had never fully seated the push rod into the MC piston I was relieved it was a simple fix.