You can get a gauge for measuring the pressure for a few bucks from any auto parts store (or Harbor Freight), and sometimes they are set up to measure vacuum as well. Very useful thing to have.
I'm using plain ol' H1 carbs, but I'd expect the same thing to be true of Webers. You just need enough flow to keep the float bowl full, and enough pressure to move the fuel through the lines and get it up to the carbs, which isn't much. I wrote up an article for the Wiki, under "General Technical Articles" on installing a fuel pump. It might be a little too much information, but it's there in any case.
By the way, a quart per minute is plenty of flow for these cars. Think of it this way--that's 15 gallons per hour. If you get 30 MPG, that'll support a constant speed of 450 MPH. I know, that's not enough for some of you, but for me it'll do.