The only thing about the 1/4 mile equation (if I remember right) is it's also based on a 'fixed' (assumed 'constant') .50 drag coefficient...(and, interestingly enough .50 c/d seems to be more or less average for a mid size late 60's early 70's car)

So, a theoretical 1968 and a 2002 Camaro at the same weight running the same ET and MPH (lets say 3000 pounds and 11 flat at 120 mph) might have the same "theoretical" RWHP and FWHP, but since the 68 Camaro has a c/d of ~.50 and the 2002 is only about .29, the 68 likely needs another 35 or so HP to push through the wind on the big end.

There is a frontal area 'compensation i.e. (< or >.50)factor' I found once on the internet, it may even be in the Wallace charts.