1. All production engines are marked MC16

2. MC18 onwards engines bolt into '18's, '21's and '28's. The '16 motor uses a different rear lug.

3. All can be rebuilt, the chances of finding a good one lay with '21's and 28's. No the NSR crank isnt like the RS one.

4. MC16 and 18 use a seperate seal, the 21 and 28 use the same integral seal but cant be swaped with 16/18.

5. Mc16/18 gear boxes are the same, '21 and 28 are the same. All can be interchanged though.

Electics wise there are just so many variables.... some 16 stuff can work with 18's. no '16 stuff works with a '28 (infact 28 stuff just doesnt work even on a 28 ). Some late '18 fly wheels will work on '21. etc etc.

All reeds are the same. MC16 uses small inlets, MC18 uses inlets with integral rec's, MC21 uses same reed block as a '18 less the rec's. Mc28 uses a different one withoiy boost bottles.
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If I have to take the carbs off once more...