A friend had a Honker bipe, back in the mid 70's...he had a Super Tigre .23 on it, and it was adequitely powered. Of your engines you list, I would think the Irvine .25 would work nicely. Modern radio equipment is significantly lighter, so I wouldn't think you'd need more than the .25 to fly it well?

I would use a light covering material to keep the weight down. Since the wings are virtually all Balsa, you don't need to do much other than to seal out the exh. residue...