Neal beat me to it!

You can mix'n'match primary gears, so long as you use the corresponding clutch gear too. So, if all you are changing is the transmission, there's no need to use an MC21 primary.

MC21 6th is 1.083 (24/26), and MC28 is 1.00 (25/25).

You can see the differences between the MC21 and MC28 here: NSR250 Specifications.
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Andy.
NSR-WORLD.COM

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