Just to be helpful I'm going to throw some weights out for the Moki 1.80 glow engine.

Engine: 42 ounces
Mount: 6 ounces (H9 alum ultra mount)
Pitts muffler: 6 ounces
Wood 18x8 prop: 2.5 ounces
3.5 inch spinner and adapter: 4 ounces

Total = 60.5 ounces = 3.78 pounds

So add that to the 11.7 pounds and you get: 15.48 pounds. That sounds a little heavy to me. I would think that ARF would come out to around 13-14 pounds with the Moki. So if you put a Moki gasoline engine plan on another half pound total for the ignition and battery. Did you mean gasoline? It will have less power than a glow, so 30cc or 1.80 is not enough power for any aggressive aerobatics. A 40 or 50 cc gas engine will be about 10 ounces heavier than a Moki 1.80 glow.

BTW, I have a Kangke CAP 232 120 about the same size as the CAP X. It has a Moki 1.80 in it and weighs 14 pounds. It has PLENTY of power and the engine is heavier than the Saito 180 so the added nose weight helps. I also had a Saito 180 in mine and went to the Moki. It's a perfect engine for your CAP. You can run 0% nitro for $9.50 a gallon and it burns very slow. You will use less than half the fuel that the Saito uses eaily. And way more power.