Chevy guys N girls i have a 408 sbc i need carb advice?
Most dual quad intakes were designed to use Holley 4160's because they have no metering block on the secondary side and are more compact than the 4150, giving more clearance.
If it were me, I'd use a pair of 525 cfm Barry Grant Road Demon Jr carbs. The secondary side has a fixed-jet metering plate, which in conjunction with the float bowl configuration allows for a shorter overall length. This allows the Road Demon Jr to fit on most inline dual quad manifolds originally designed for dual 4160 Holley carbs.