RE: Another "What engine" question for a 4*120
You can convert a Ryobi 31cc weedwacker for about $50--$75.
Move the firewall back and slap it on there. Mount your elevator servos in the tail and maybe the rudder servo as well.
Beef up the LG mount.
Use a 10--12oz tank and fly it with the Ryboi for pennies compared to a glow engine.