Bill D,
If no one with the exact setup you have comes by, perhaps this website can give you some insight:
Brake Calculator
Eventually you will have to decide what combination of pedal pressure and pedal travel feels best to you. A smaller diameter master cylinder will reduce the amount of pressure you have to apply, but the pedal will have to travel farther to push enough fluid to move the calipers sufficiently. So in your case, you'd use the calculator to enter the fixed data (e.g., caliper diameter and pedal ratio), add the pedal pressure / travel you'd like and see what master cylinder diameter is required.