Just discovered another person has already done what I had in mind here. Sounds like you can get a Sikk 29cc converted for aircraft use with CH ign installed & ready to run. See [link=http://www.rcuniverse.com/forum/fb.asp?m=2270688]this message[/link]. The prop RPM's look pretty encouraging.
The entire flywheel housing has been milled off. This is exactly what I have done to my 27cc motor - right down to the standoffs and mounting plate. I'm using Ralph's ign and a Wacker muffler for initial testing. I also just ordered a 29cc engine from DDM, so I will be doing side-by-side testing of the two engines.