Brian. You are correct about the piston being different. I have heard from Ken Enya. This is what he said:
If you would like to convert to 61CXLRS from 61CXRS,
you have to change
crank case, piston,
------------------------------------------------------
1 x crank case (without bearing) (61CXLR03A) = JPY 4,700
or
1 x crank case (with bearing) (61CXLR03) = JPY 6,450
and
1 x piston (61CXLR04B) = JPY 2,400
I have now set about ordering the parts.
Thanks for the reply and detailed information Brian.