Before storing the plane after flying... run the remaining fuel out of the engine. get the engine running full throttle and pull the fuel line. That prevents most of the accumulation of oil in the glow plug. (can also pull the plug....) Then put some after-run oil in and flip the prop a few times.

Not bad advice for upright or inverted... but more imortant for inverted mounted engines.

When the engine is running, and properly tuned... it doesn't care which way is up. Starting an inverted engine requires more care to avoid flooding.

That's about it. Mount it the way you want.