If those engines were not 'tweaked' a little I will eat my socks!
I once took a pretty stock (except for slightly hotter cam) 440 4bbl Challenger with 3.23:1 gears and only just made the high 14s. Remember that was with a hotter cam.
I can't see a real stock 6pack or hemi going that much faster. But all the companies were tuning the 'magazine' road test cars because they knew a good write-up about the performance would sell the cars better than how well built (or not!) they were.