Darn it
I finally get to take a poke at you for going over to the 4 stroke dark side, and you find a good way to blow me off. Crap.
Seriously, I can see no good reason to add the weight of a pipe on a 4 stroke, as you will see no performance increase. If a minor aerodynamic increase is worth the trouble you could probably make a pipe that fits close to the fuselage and fair it in.
Since you made a mold, I would probably consider making a fuselage out of carbon fiber and vacuum bagging it in the mold. I am sure you could shave several ounces there. You would just need to figure out how to make the radio work. Some external antennas would do it, but you would need accurate information from someone who knows more than I about it. I could help you with a layup for maximum strength and minimum weight if you want to go all carbon fiber, but you need to solve the radio problem.
Cool plane. Keep us posted.
Scott