Hi Mike,
Why don't you upload a picture of it. I think it is a trimmer engine. McCulloch trimmer engines came in three types that I know of. The most common are the 28cc and 32cc engines. they make good airplane motor, but are on the heavy side. Then there are the rebadged Poulan/Weedeater engines that have been seen in Europe. Also there are the Echo/Kioritz style Mac's which are 18 to 21cc. They all can be converted to plane use.

Dave