I'm thinking that the mid 70's master should have a heavy rubber o-ring or bushing that the rod pushes into to keep it centered and secure. If it was for a manual (non power assist) braking system. I've changed many that you had to literally use both hands and with your chest across the wheel, and a mighty heave ho to rip the rod from the master. Some used a metal clip with "fingers" to latch onto the rod and others used a rubber or plastic o-ring/bushing to hold onto the rod. Again, this is only for manual masters..See if you can't look up inside the master bore and tell if there is a rubber / plastic piece in there or a circle clip of fingers? Or maybe a place for them??