SM,
The plane is designed for .90 to 1.08 glow or a 1.20 4C. They have a plywood box to add a bunch of weight to the nose for balance. It has a nice large firewall and almost 1500 sq inch wing area, so any thing from 25 to 40cc gas will work fine. Don't forget to add flying wires for the larger engines to beef up the firewall structure.

Dave