What you will need is their single caliper master cylinder. I think these are 16x18 and 16x16 ratios. It's not wise to use the 2 disc set-ups which are 19x20 and 19x18 bore ratios.

I went for the 19x18 as it gives a better feel at the lever, especially with a lighter bike. These are standard size on modern RS250's for instance. The 19x20 would have given to little lever travel for the same braking force.

A similar principal exists for the single caliper set-ups.
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NSR300R - Why did i ever have a 250...