Thanks Robert, I appreciate the response.
I am a newbie, so there is a lot I don't know. I read and was told that with all brake drums, the dual chambers on the master cylinder would be the same size. This might not be true, and based upon what you have in yours, seems to prove it isn't true. But even looking at the link you send, all the master cylinders for applications with disc brakes up front appear to have a larger chamber for the front than for the drums in the back. The ones with drums all around, have what appears to be, equal size chambers. Including the one Mike mayben suggested for a 73.
As you know, my brake set-up was a single chamber master cylinder, so going back to the original setup, which would be "correct" for my setup, imho. Is a mistake in safety.
Of course, I am looking at this grossly and I know there much more at play that simple chamber size. So I appreciate your help and continue try to learn more and to look for a solution!