SARGE - ROAD WARRIOR

Before the Cardone unit failed, the brakes were perfect. The M/C started leaking at the booster. Ever since, I have been fighting an uphill battle and losing. Numerous M/C, three different boosters. The unit that worked came from a 69 C20 pickup. That unit is hard to find.
I have gone from brakes that grabbed each time you stepped on the pedal to what I have now. Mushy pedal which goes to the floor and only the back brakes working. The shop tells me that they are looking for a M/C with a larger bore in hopes of increasing the volume of fluid going to the front brakes.

 

A larger bore master cylinder will certainly move more fluid per unit of linear travel and take less travel to full lock up. Do you know what bore the '69 C20 master cylinder is? Why did it require such an obscure master cylinder? There have to be other more available options that could be used.