Anyone care to compile a list of the engine parts that are interchangeable on the 200cc engines? Iíve learned a lot but have far to go. The M model is the one I donít have for reference.
Some are the same. Some are not. Obviously 200x is excluded.

I know all the top ends are interchangeable.

My assumption.
All right side case covers are the same?
All right side case spacers are the same?
All left side case covers are the same for electric start models?
Left side spacers are different for E & ES and do not fit left side main cases for S & M models
Clutch baskets and centrifugal clutches are all the same.

Some engines have different gear ratios. Can those be swapped around to build a custom 1-5 gear ratio?

Be nice to have this information.
I have an engine I plan to build based on the 200m bottom end.
I could really get a jump on the game cleaning, painting, and replacing bearings on parts I already have.