Its not a easy swap. The RS crank has a shorted taper as it uses a different gen, it also uses a 14mm piston pin (compaired to the NSR's 15mm). This would mean using RS pistons (single ring). This then involves remachining the barrels as the RS pistons are shorter than NSR pistons as well.

Its much easyer just to have the old crank rebuilt.
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If I have to take the carbs off once more...