I spent some time talking to a guy that raced 68 W31's (ramrod 350) for Oldsmobile. The 68 cars used two ducts routed to scoops under the front bumper. He did a good bit of testing and reported that this was worth significant ET and MPH improvement. He did mention that the scoop-under the bumper design on the 68 cars where more effective than the sealed hood scoop design used on the 70 cars.

Also, aside from any increased intake pressure effect, we know a cooler intake charge is beneficial.