Kevin, these cars can be
really twitchy, and it's easy to get in over your head before you even know it.
Considering you've not driven a 500+ HP, 2500 lb. 90" wheelbase car before, my recommendation -- and please don't take offense -- is that you have your engine builder zip tie your vacuum secondaries closed, or if they're mechanical then disconnect the linkage, after he breaks it in and tunes it up nicely. Drive it that way for a good while until you get used to the car and then snip the zip tie or hook the linkage back up.