I can tell you for sure ... I don't have a "half inch" of clearance on mine.
My pickup has a metal strip/spacer which insures (and I'm guessing here, it's been two years since I assembled my 351C) anyway, about 1/4 " of clearance. When I checked for clearance without pan gaskets this spacer barely hit the botton of the pan. I figured that once the gaskets were in place and the pan tightened down, I would have sufficient clearance. Spacer will insure that pan can't "suck up" to the pickup.
If I had a half an inch clearance ... I'm guessing I'd have nearly 3 quarts of oil in the bottom of the pan that would not be available to the engine ... Not exactly the idea behind a 9 quart oil pan.
Obviously, you need enough clearance to allow the pickup to gather oil at a rate atleast equal to the ability of the pump to "pump it". But in my opinion, common sense and the laws for physics and geometry tell me ... there is no need to have it higher than that.
Also, the higher it is ... The more likely it is that you could have problems with the pump sucking air under hard excelleration or cornering.
My two cents
_________________
Larry Madsen
Las Vegas Nevada
<font size=-1>[ This Message was edited by: monstermach on 2/9/02 8:09am ]</font>
<font size=-1>[ This Message was edited by: monstermach on 2/9/02 8:14am ]</font>