You could even consider a .30 size 4-stroke.

I have an old Kadet Senorita (63" wing) that flies real well on a .26 4-stroke. Of course, it is an exercise in "flying on the wing" rather than brute power - no unlimited vertical here.

Again, as was mentioned above, check out the weights of all the possible engines. With the dihedral, it sounds like a good trainer type and you don't want to go turniing it into a lead sled.

Take care, and let us know what you end up doing and how it comes out.