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
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>
I have my car apart right now, replacing the oil pan, clutch, front cover etc. I saw your post and measured the clearence I have with my new Canton oil pan and pickup, if I measured right the pickup is 1/2" from the bottom of the pan.
About the 9 quart oil pan- I believe that oil is available to circulate just as the oil above it is, just not all at once. All 9 quarts will circulate as oil from the upper engine returns to the pan. The extra oil helps dissipate some heat and insure there is always fresh oil available to the pickup. Also, you have to consider that the resistance of any fluid to flow is greatest near any surface it contacts. (according to principles of fluid dynamics) The clearance is needed to move the pickup away from the oil pan surface which allows the oil to flow more freely.