doing a bit of math, the original bore was 1 1/4", but that 1 1/4" fed all 4 wheels. Since you are using a dual cylinder, you want roughly half the volume on each cylinder (probably more like 65-70% on the rear since, like on mine, I have 2 cylinders on each rear wheel and one on each front) but you get the idea.
I think you are probably fairly close and are on the right track with adding a booster. Once yo uadd a booster, you may want to put the larger bore master back on.
