Not enough information to give you any recommendations.
We need to know what airplane, ie.. trainer, sport, scale ect...
Wingspan vs engine size is much different from a trainer to a scale warbird. Example: 80" wingspan trainer can fly on a .46 size (7.5cc) 2 stroke glow engine. 80" wingspan P-51 you are looking at about a 50cc gas engine. Huge difference.
How much does it weigh?
What size are the engines you have?
What model Futaba?
Pictures will help.