I ran 2 Holley 600's on a 350 for years. I made sheet metal plates between two gaskets that blokced off the secondaries butterflies of both carbs, soldered the fuel transfer tube shut and ran progressive linkage. I did this so I could use both accelerator pumps on WOT .
The engine ran very crisp after I got it fine tuned and it got suprisingly good gas mileage on what was essentially a two barrel. I did have to monitor the rear cyllinder spark plugs so as not to go too lean because of the tnunnel ram airflow situation.