Block from the outside in and the top down. You want the opening to be as low and centered as possible for the best aero gain. Cooling systems are designed for a car fully loaded, going up a mountain, with a tailwind, on a 120 degree day, and behind a semi truck.
Sorry if I offend, it is really not my intention, but in looking at the 67 Chevy, the grill area is sloping the wrong way for proper aero dynamics. We want as much of the air to go over the top of the car as possible, not under. It isn't the absolute worst aero front end you could design, but it's close.