You never mentioned the engine you will be using or what type of CUB. If a four stroke, I have been told they are much better at running inverted, Two strokes are much less so. The two strokes glow plug will be sitting in a sump, when inverted. Four strokes are generally off to the side and higher up on the cylinder head, when inverted.

It's your call on whether to invert, or not. Fully cowling an engine has it's disadvantages, also! Are you going to compete with the cub or not. Even if competing, judges don't discount for having a cylinder head sticking out of the cowl. Side mounting points the exhaust down, helping with clean-up.

Personally, I will avoid inverting at all costs! However, that is me and it appears designers seem to think inverting is the way to go! I don't think much of designers, which will design an airplane that will use an inverted two stroke.