I'm still waiting for a reply from Apex but a new and maybe better idea has entered the picture!
A buddy called yesterday and asked if I could come by his shop and help for a few minutes. I was walking through his shop and noticed a clutch/brake pedal assembly laying in the floor and asked him what it was for......he said it was for a 2011 mustang. Later in the day, I got to thinking about the assembly and thought it might hold the perfect solution to the 71-73 mustang clutch master cylinder problem I am working on.
I went back today and took a bunch of measurements and photos......my conclusion........I believe this clutch master cylinder is a simple and ridiculously easy solution. For those who don't know, on these cars, the clutch master is mounted to the pedal assembly under the dash. From what I can tell, the same master is used from 2005 to at least 2014, so they are common and relatively inexpensive.
I took the clutch/brake pedal assembly for the '73 with me and did some measuring and comparison. I measured the distance from the clutch pedal pivot to the pin for the master cylinder, the overall length of the master cylinder and piston rod, the stroke length and the angle of the master cylinder mounting.
Everything I have seen so far tells me that a simple bracket is all it would take to mount this master cylinder to the pedal assembly for the '73. Mounting the master cylinder under the dash will allow retention of the factory brake booster and access to the clutch master for service should be easier on the '73 than on the 2011.
I still need to do some research to find out if this master cylinder will put out the correct volume of fluid for the hydraulic throwout bearing I will be using (4th gen GM f-body T56)......if that proves to be compatible, I will move forward with building the bracket to mount the cylinder, drilling the clutch pedal at the correct location and making a pin and spacer to attach the piston rod. I will try to document everything for those who are interested.