Re: Slow oil burn
To check for valve stem seal leaks, you can also coast down a hill, or coast to a stop, and then observe the exhaust for a puff of blue smoke when you accelerate from a stop. The coasting will cause higher vacuum in the intake, and increased suction pulling the oil past the seals.
Consumption at that rate is totally within acceptable FoMoCo norms. Their unpublished limit is 1 quart in 600 miles. You beat that significantly.
Look at the oil pan gasket, front and rear seals, and rocker arm cover gaskets for seepage. The pan is noted for being difficult to seal, but new and 'improved' gasketry is available.