Have some questions.

Rumblefish, you said I want the vacuum gauge to drop to zero at WOT, what would that do for the brakes if I need them?

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Well, if you attempt a 4 wheel lock up while traveling at speed with the right foot on the floor.....Wait, normal people don't do that.
Once your foot lifts off the gas, vacuum returns. Full brakes return.

If you opt of a smaller cam and less gear than 3.90's, I'd go with the 670.
Otherwise, the higher stall, larger cam and 3.90's, 4.10's etc... describe a different car than one with 3.73, 3.55's and a milder cam.
While you could use a larger carb, it isn't really needed. The 670 is more inline with the engine than the 770 would be.
The idea being to keep a well balance package.