Reading your reply, Its even more obvious that the issue is low oil pressure. Thats why the hydroulic lifters shut up when the light goes out, because the pressure has rissen and pumped up the lifters to close down the rocker gap. So you need to be looking at why your loosing oil pressure, not worrying about the polished cams. If the pickup pipes definatly not blocked, then that only leaves the pump. If its worn it might not be priming itself and pumping properly?
Your not still using the pickup pipe with the hole drilled in it are you? That would cause you to loose suction from the strainer in the oil and just pull air through the hole if its above the oil level. That would also explain why parked on the curb it dosent occur, the oil might be over the hole at that angle? On another note, if youve had the strainer off, how does it connect to the block or pump, is there a seal, and is it intact, again, if its not got a good seal you will get an air leak and loose vacume to properly suck up the oil, youll be sucking air instead.
One last idea and its a bit far fetched but have you checked the oil filter and fillter cap. The filter should be pushed by a spring in the cap down into the block, so that the point on the filter with the rubber o-ring round it seals the center hole in the block. The filter raises up out the hole with oil pressure and acts as a kind of one way valve come pressure regulator. It also helps keep the pump primed. Quite easy to check and actually it could be the problem, especially if youve used a cheap aftermarket filter. easy enough to take out and examine.