The residual pressure valve is easily removed with an easy procedure. I went out and did one for ya in one of my mockup/visual aid master cylinders
..took about 5 minutes, including taking pics.
Tap the male flare seat with a 6-32 tap.
Screw a nut onto a 1" x 6-32 screw, stack up enough washers on the screw to keep the nut from falling into the port, then screw the whole stack into the tapped port.
Crank down on the nut and that seat will pop right out.
Remove the RPV valve and spring, (you will see that the RPV prevents the chips from tapping from going in the bore) clean everything with a bit of brakekleen, then reinstall the brass seat. You can seat the brass seat with a tubenut of the appropriate size.
You can probably run that 1" mc for a while, if it develps enough volume, but a 1 1/8" might be necessary. You'll have a low pedal with the 1", but you can see what the pedal effort is like.
Later, mikey