Older trucks are certainly not as aerodynamic as the current trucks. Things like flush side glass and no drip rails, and smoother blended surfaces all combine to make a newer truck more slippery. But in frontal area, the barn door effect is pretty equal. Think of shining a bright light straight at the front end onto a bright surface behind the truck, the shadow outlines the total frontal area. The older truck, especially a lowered truck, likely presents a smaller/lower frontal area than many of the newer trucks.

I'll have to compare the overall package of a 4.7HO versus a crate 318/5.2 Magnum versus a crate 360/5.9 Magnum.