A Lycoming or Continental carburated engine will run very poorly lean of peak.
Not if you know what you're doing. A horizontally opposed continental or lycoming runs very well lean of peak.
In fact, one wonders why any multi-row radial in a taildragger doesn't also have the same oil-in-the-intake-pipe problem.
They do, just like any radial. Various run-arounds have been devised address the problem, but the bottom line is that in a radial, oil bleeds past the valve guides and eventually floods lower cylinders.