I recently acquired a 350 jumbo in very nice shape.  It has been ridden quite a bit, so I took the top end apart.  The piston and cylinder look amazingly good (I did measure with my gages and the cylinder is still within spec. for a cylinder of this size).  But, the end ring gaps are about 20 -22 thou.  I'm getting the piston coated with an abrasive powder coating product that they use in very high performance/horsepower engines. been doing this to all my bikes for 10 years and have had amazing results.  So, does anyone know if OEM standard,1st or 2nd over piston rings are available?  They would be an 82.0mm, 82.25mm or 82.50 mm... as needed, I'd file down to fit.  From what I found the part numbers for a 1st over would be 215-301 and 215-351. Or, what other Rotax engines share this size?  Thanks.     

Any comment/feedback appreciated.