RS cylinders just bolt on, the volume may be slightly tight with NSR pistons, it's way too loose with RM125 (single ring) pistons but if you're using RS bits you'll be checking such stuff anyway, a badly assembled RS would be beaten by a well assembled stock ported NSR every day of the week.
Obviously stock RS pistons have a 14mm piston pin and thus can't be used.
You will need all the RS RC valve pulley mech.
You'll have to do something about the pipes, the RS has a three bolt flange.

The RS crank (of the correct age?) fits the early mc18 cases.

If you machine the cases you can use the RS adjustable flyweel and tiny stator, details of what to machine are in the mc18 f3 manual but if you've got the flywheel, stator and it's backplate it's obvious.
The flywheel fits the NSR crank.

There is no reason an engine like the one above won't run very well on the RS pipes, carbs and all electrics.
It's been my finding (only from 2 bikes so this may not be conclusive) that the RS PGM-II works OK on a stock NSR motor if that NSR is running RS pipes. It's rubbish on NSR pipes, the KV3 (mc18) PGM-II is 5 bhp better at the top and stronger all the way up too.

Be aware that the RS loom and CDI does not have any provision for the air solenoids or TPS. Likewise the RS carbs don't have a TPS on so if you run the RS carbs and a stock NSR PGM the RC valves don't work as they just sit in the "set" position.

It's a shame I can't mod this forum as this topic wants splitting now.
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