Well, yeah . . Normally, we speak in generalities here unless someone puts up specific dimensions . . and of course, most of us understand you can't pull vacuum if you have a screen door for a pan gasket . . (Tongue in cheek here) . . Or no cylinder pressure . . Got leak down? Then you are gonna have a hellova time pulling a lot of Vacuum . .
No, all your other ducks gotta be lined up for either a Vacuum Pump or an external Oil Pump to pull high vacuum . . That is, or should be an "Understood" . .
On the HP gains, Hedrick Racing says high vacuum lowers the pressure on the bottoms of Pistons on the downstroke, and if your scavenge is functioning correctly, it eliminates the HP robbing Windage almost completely . .