The gassers are getting increasingly smaller and lighter , but they`re not as light as a Saito 100 yet and still behind glow powerwise.
If your plane can`t take the weight of a normal gasser then you could "gassify" (I just invented that word) a normal glow engine. My friend "yallaair" have just recently converted his OS 120 AX to run on gas. The ignitions are cheap from www.hobbycity.com or www.justengines.unseen.org and it is no big deal to put it together. His AX runs beautiful after some trying and error with the spark timing.
The same could be done to all glow engines, smaller or bigger, two or fourstroke (not the YS engines because of silicone parts inside)