Dave:

Look in the exhaust port. If the vertical parts you see around the cylinder are steel colored, and there is a grey ring around the piston about 1/16" from the top with the grey ring also about 1/16" wide, you have the ringed engine.

If the vertical parts you see are brass colored, the engine is ABC. Highly improbable, as Ed M. said.

If the vertical parts are sort of tarnished silver colored, it is ABN.

Hope this helps.

Bill.