Theoretically if your engine is an OS and properly tuned you can run it inverted with no problem or need for on-board glow driver.

My experience with inverted engines, although only OS, tells me that it is best to avoid placing your engine this way as much as possible. Idling and transition will not be at their best.

However, if your model does not permit other than inverted engine position -I think this is not the case with Cub- you will definitely have to sacrifice "clock" idling if not using on-board glow.

Stelios