Some turbos actually have true mechanical seals that will hold back full oil pressure.
I ran a garrett on a 914 I built in a pull through application (turbo was after a carburetor and before the engine). In that application a mechanical seal was manditory because the turbo saw full manifold vacuum when the throttle was closed.
A turbo like that would actually be better on a 911 but the piston ring type will also work as long as the oil is drained away fast enough to prevent a level from building up in the drain section.

yes you can, i used a gauge on the inlets of the turbo when drilling custom restrictors to monitor the pressure.

This may be so simple that it's rediculous BUT I was having the same problem with my 3.2 with stage 1 ,so much smoke that the neighbors were laughing !! ,it had been standing for almost 3 years so I was convinced that turbo ,valve guides/seals ,oil rings were all shot.........on the advice of a few of the people here ,I dropped 1.5 qts of oil from the tank and VOILA....not a drop of smoke.......my oil return is also gravity with very little height difference.
Sam.