Redfox is right, either way is fine. The .72 will be way plenty power, you won't have to work it hard, so don't worry about overheating. The two oval cutouts in the front of the cowl, plus the area around the prop hub, should allow plenty of air in, unless you're going to try hovering. Just make sure the outlet underneath is larger in area than the inlets. Here are some pics of my Sig 1/5 scale, weighs 10 pounds and flies great with a .65 Saito. I haven't had any overheating problems with mine, nor any of the stuff you hear about inverted engines. I do recommend either an on-board glow or remote glow starter attachment if you invert the engine, as the plug is difficult to get to. Note the scale fuel filler as redfox suggested: