OK... the fix is in!
Since we were able to crank up nearly 30 lbs oil pressure on a shop gauge with a drill, we knew insufficient oil pressure was not our problem. The only logical explanation remaining was that we were bleeding oil internally someplace. After examining the interior of the block for anything obvious, we checked the fit of the cam to the bushing and it seemed snug enough. The next opportunity for excessive loss was the drain hole behind the cam bushing. So...
We drove the cam bushing to the rear a little more to partially cover the drain hole. Then we reversed the cam plug and drove it in sufficient to partially block the same hole from the opposite direction (all told, about 75% covered). Reinstalled the cam, cranked up the drill and... WHALLA! Ample oil now flowing to the lifter galley and through the oil line to the rockers.
Not exactly a "text book" fix you'd read in a shop manual, but it worked. Hope someone in the future finds it useful...
