Anybody bothered to check out the Mormon Missle underbody, or from a couple yeas back, the Haas entry (BGS?) or the Eyebal Engineering Electric and the later Dempsey Electric from ten years ago?.
Those designs, by Gerald Arivett, had FRONT and REAR tunnels, and the cars run relatively low but not flat. The electric designs were tested in the now defunct Galcit wind tunnel.
Bill Scott's quick and dirty built lakester had a large tunnel out the underside and when originally built by the Arivett Bros., had the exhaust dumping into it. (Like today's Formula One). BILL DIDN'T LIKE IT BECAUSE HE COULDN'T HEAR THE ENGINE!!???! There's a Harnick picture from a few years back at Elmo of Bill in the traps and a HUGE dirt cloud pouring outward and upward from the tunnel. Look it up!
The Missle used the Arivett/Haas molds slightly modified.
Don Ferguson owns the molds for all but the Eyeball car, which is an Arivett/Scott Knight aluminum body.
Besides the excellent book by Dr Katz, people overlook Forbes Aird's (interseting name!) book Aerodynamics for Sports and Racing cars. Not math heavy and Aird explains aero phenomena in understandable terms.
Read the dissertation on Drag Race parachutes - surprising in the conclusions drawn! He has an example or two and opinions on LandSpeed "chutes.
Incidentally Gerald has two 1/4 scale models in development for wind tunnel testing currently.