serious interference would be the prop wash
beating
against the airplane itself? I'd have thought we'd see more pusher props,
but
that's not a common SEL configuration either. I wonder why?

Pusher props are only *theoretically* more efficient. Since the airframe
disturbs airflow into the prop, you just wind up with a different kind of
inefficiency. Also, there's the problem of how to protect the prop from
ground strikes, engine cooling, CG and the like. All solveable, of course,
but the engine/prop in front configuration actually works pretty well in
most cases.

I agree with some of your observations, but re efficiency -- the airflow into
the loow pressure area around the prop comes from pretty much everywhere, but
the exit flow is directed backwards. I think props don't get much thrust from
'suck' as opposed to 'push'. I suppose my model's example would be to stand a
few feet in front of a fan, then a few feet behind it.

Didn't the Skymaster do better with the rear prop, and the Rutan around the
world airplane?

The other issues re having the engine visit the cockpit during a crash surely
bear thinking about.

It's also true that propwash does a good job of keeping the Mooney's windscreen
clear during rain.