The people who sell the disc brake conversion "kits" ( I detest that word!) use power boosters for various Japanese vehicles- - - -don't remember which ones at the moment, but I believe most of them are around 7" in diameter. Since all a booster does is use vacuum to make the driver's leg stronger, it's not rocket surgery to cobble up a booster/master cylinder combination that will work with your existing single line brake system. I believe there's also a small diameter booster that fits some Corvettes. A master cylinder with about 1/8" more diameter than original will move more fluid with a shorter pedal stroke, but it will require more pedal effort. That's where the booster comes in.
Jerry
