Hi Walter, thank you for your kind offer.
I received this engine in a trade, and didn't really have a chance to take a close look until after the weekend. A closer examination showed that while it was pretty clean on the outside, the conrod was shot, and the internals revealed lots of hot runs. The fact that it came with an RC carburetor tells me it might have been fed RC fuel and forced to turn at higher RPM than it was designed for.
I will be returning the engine to the original owner, so no need for a muffler.
However, your willingness to come to a fellow stunter's help shows why our community is great. Thank you again!