350 cubic inches at 4,000 rpm's will flow 364 cfm at 90% efficiency, which is probably a stretch for a stock 350. It's probably more like 80% efficiency and 324 cfm, so a 600 carb is way overkill. If it were mine, I'd get some books on the Quadrajet and rebuild it. It's probably the finest 4-bbl carb ever built and the tiny little primaries will give better mileage than the larger primaries on an E-brock carb. That's just my opinion, what do I know?