What's he using to create or pump Vacuum? A "Vac-u-Pan system, installed right will pull maybe 4-5 inches on a good day, if he's got his cylinders sealed really good (Good rings, seated, etc) and all his gaskets are working . . If that's all he's using, a really good oil pan is necessary to keep crankshaft windage at a minimum . .
But that's all old technology and if he wants to make the next step, a vacuum pump is pretty necessary . . With a good pump you can pull 7-14 inches and that will work pretty good . . But you still need a good oil pan/scraper to keep the windage down . .
The Engineers claim (and I believe them) that windage in an Engine will require (or use) 35 to 125 HP of parasitic loss. Deeper oil pans with efficient scrapers and directed oil returns lessen the drag of windage around the crank, and you get HP in return. They don't "Make" HP, they just "Free" it up . .
We finally went to the Dry Sump for several reasons . . one, it eliminates 95% of the windage in the engine. Two, it bulletproofs the Oiling system. Three, if, for some reason, you window the block/pan, the diaper doesn't have the large amount of oil to keep off the race track in front of your rear tires that an 8 qt sump would . . And four, it makes a lot of people who race with us look in the engine compartment and say; "WTF?"
Granted, it's kind of 'spensive, but what's your head worth? (Old Crash Helmet question)