My 1996 F3 front brake piston size measures 25.4 mm diameter, both pistons.
I bought a 2001 F4i front brake and the piston measures 31.8 mm diameter for the first piston and the second piston measures 33.68 mm diameter.

I started making a cardboard bracket and then I tried 1/4 inch plywood.
I think for the next try it will be clear plastic so I can see thru it. Its difficult to hold the caliper with one hand while the other hand is trying to mark the cardboard. Its going to take a few tries until I satisfied with in. I don't know if the final bracket is going to be made with steel or aluminum (6061 or 7075 alloy). This is going to be my winter project.

 

Sounds like an interesting winter project. How do the rotors compare between the two bikes as it relates to the surface area where the pads rub ?

I'm curious if anyone here is able to do a Stoppie with their factory brakes ? If so, is there really any need for more braking power ?

 

Rotor diameters are exactly the same. Other possibilities honda goldwing, same size rotor, 6 piston. Other possibilities 96/99 gsxr, 98/99 kawasaki, 05/08 zx6. Master cylinder size is the same between f3 and f4/f4i.