RE: Suggestions for L-4 Cub motor
I'm assuming that the Cub is 1/5 scale, or thereabout (84.5 in. wingspan is 1/5 scale). If so, anything in the .56 to .70 range will fly it (4-stroke). I have the Sig 1/5 and have a .65 Saito in it, mounted inverted. The only visible part of the engine is the tops of the valve covers, the rest is completely within the cowl (see pics). Now, the .65 is no longer made, but the newer .62 is the same size as the .56 and is shorter from crank to valve cover than the .65. It should conceal very well inside the cowl if you invert it. The small holes in the front of the Cub cowl should be enough to allow cooling air in, just make sure you have an outlet that is about 1.5 to 2 times larger. I haven't had any problems with mine overheating. To allow the exhaust to exit the bottom of the cowl, you may need to find some kind of 90 degree fitting, or find one of the older style 90 degree elbows.
The glow plug will be difficult to get at with the engine inverted, so either an on-board glow, or a remote plug will be a big help.
The other thing is measuring from the firewall to the prop hub with the engine mount you want to use. I used a DuBro antivibe mount and had to recess the firewall a bit.