KW,
A Sears Craftsman 55cc saw engine may be the answer for you. Combine it with a 80" or larger ARF. Make sure that your flying and building skills are up to the task. If not practice some more on the small ships. Here is the link. Electric ignition would be required for lowest weight.

http://www.rcuniverse.com/forum/m_49...tm.htm#4924641

Dave