Set the initial timing with the vacuum advance unhooked and plugged. Once that is set hook the vacuum advance back up. Vacuum advance is for economy for driving around town. At WOT you have no vacuum, thus no vacuum advance. At that point its all mechanical.
If your friend is only into high performance cars, he might be used to just running vehicles with mechanical advance, with no concern for street driving.
Since it is a street car, you want to use vacuum advance. It wont affect your WOT performance.
As long as the timing was set with it unhooked and plugged (and at the right timing spec), you should be able to plug it back in. I'd suggest getting a book or doing some reading online about timing. It really isn't that difficult to learn.
Bringing history and technology together.