Hi,
I have an engine on the bench now that is exactly the same. I took it out of a Weedeater BV-200 leave blower. Mine is a 25cc, single pined ring with a 10mm Zama carb. It has a four bolt backplate, bolt on muffler and a long shaft (5/16x24) with a flat milled on the shaft. The hub used for the impeller is well suited to convert to prop use. It uses a washer at the flywheel, a steel tube spacer and a keyed impeller driver that can be cut down to make a great prop hub. You just cut off the portion that keys into the impleller. When done you will have a powerful long shaft 25cc airplane engine at about 3.5 pounds with mag. The carb is the correct size at 10mm, but the exhust is on the small side. Mine has a aluminum slevve in the exhust, when removed it leaves a 1/16th lip accross the top of the exhust,flish with the bore. It would be very easy to remove this material and chanfer the port edges to enlarge the port and advance exhust timing. I need to throw a degree wheel on it to find out where I am now and how much material needs to be removed. The idea is to match the stock Homelite timing to start. It will be a little weak with existing timing. The compression can be easily increased, because the cylinder doesn't have a flange and is flat on the bottom. This allow it to be milled or filed carefully down after taking measurements. It looks like a great engine for conversion.

Dave