master cylinder upgrade

Why do you feel you need to upgrade?

You won't get any improvement in brake performance. If the one you have is failing just go to the local parts store and get a rebuilt one, they are around $20.

I agree with dusterdon, do a disk brake upgrade. I went from 9" drums to the 73+ disks on the front an 10 x 2.5 drums on the rear and the braking performance improvement is like night and day.