Oil smoke on startup

If I remember correctly, my friends Helicom (Safari) used to have a vertically
mounted Lycoming.

If one or more of the oil returns from the rocker covers (valve covers) are
restricted in any way oil will build up in the valve cover and leak in through
the valve to guide clearance.

Lycomings do not have valve seals, so that won't be your problem.
If the oil leak into the cylinder is severe enough, you could experience a
"hydraulic lock" while cranking the engine over.

Oil is not compressible and when the piston meets the slug of oil it usually
results in a bent rod or broken piston.