side effects of having engine mounted upsidedown compared to sideways?
Not much difference...
When you mount the engine inverted, the glow plug will get soaked with oil, when the engine hasn't run for a while, that's all.
Plus you have to be careful when priming the engine, because all fuel will flow staight into the cilinder. Make sure there isn't too much fuel in the cilinder before you attempt to start the engine, because if there is, it isn't very nice on the con rod...