Maybe you could just get a new cowl if you could figure out what plane it is? Fiberglass specialties may have a .40 size Tiger Moth cowl. I think that would look much better.
I agree with using a 4-stroke. I have a saito .56 and love it. Perfect for that type of plane. Get the best engine for the plane and just re-install the throttle cable to suit the engine. It is not difficult at all to re-rout them.