Master cylinder questions

yeah, like part number 101573 is for power brakes, 101573M is for manual brakes. I don't recall exactly what the difference is. If its only a residual pressure valve in one of the line ports that could be removed with a hex key, this might not make a difference in pedal effort. I think its the manual master cylinder that has that extra thingy.
Our 67 is still 10 inch manual drums all around. Grand daughter complains about manual brake pedal effort often. Nothing wrong with the brakes. She is simply accustom to power assist in everything else she drives.