RE: Wanted :Rossi 60-61 Piston, Sleeves
Roger,
There is more than one version of the Rossi 10 cc engine.
The bore and the stroke which I quoted, are for the 240R60E version.
It is definitely an under-square engine (what's known as 'Long Stroke') and it has bolt-through exhaust mounting.
The .61 RE engine offered until lately, was an over-square, high RPM engine; probably like the one that you own.
I know you are probably used to the Imperial system, but all European engines have nominal dimensions in millimeters.
And yes, I do believe the piston may interchange between side and rear-exhaust versions of the same stroke... But other parts may not and the sleeve is one of them.
You must make sure the spare P+L that you get, fits your particular engine.