Wilwood is saying 1" diam. for front and rear for the master cylinders and then the balance bar in the pedal assembly for tuning. I will probably not go 6 piston, as they are almost twice as heavy as the Dynalite 4 pot. If the Dynalites on the rear have 1 3/8" pistons, I'll be using 1 5/8 pistons on the front, but I have to reasearch as to what I actually have in the rear right now, they came as part of a kit I ordered and I don't know exactly what they are.
Jason