Looks like a .049 (Cox?). A good model for this engine is the DAS SPLATT. Go to Radio Control Modeler's (RCM), plan page. Plans are about 3 pounds.

http://www.rcmmagazine.com/e/env/000...nk=/index.html

While you're ordering, include the magazine's , Pilot Traiining Course, instruction manual (7 pounds).