You're not helping him, guys ... The Master cylinder will be fine .. There is about 2mm bore difference between the smallest and largest. (In fact, I had a 1986 1.3 OHV M Cyl working on a system with big rear shoes and Cosworth fronts, no problem .. until I knackered the Master Cyl bleeding them up later) Nothing to do with the power of it.
There is something major wrong with what he has done somewhere.
Make sure the brakes are adjusted up properly. Sure front calipers are correctly fitted?

Al.