Hi John,
I just got done reading your post and I must relate an opposite opinion on one piece of information. First let me say I am glad we can all come here and pass on our ideas and I will not claim myself an aerodynamics scholar, however........ After building two road racing corvettes, both with factory angled back radiators, it became apparent why this is a good idea compared to other angles. If you look at the intake designs of Ferrari, lotus, etc. you find that radiators are leaned backward to take advantage of aerodynamic curling. The same type of curling you find that causes lift on an airplane wing. This curling turns under when hitting the radiator making intake through the radiator less efficient. Leaning the radiator backward corrects this flow through the radiator and allows better cooling. The amount of forced air at high speed through the radiator is not enough to cause lift. Most is lost to the vacuum created at the back of the vehicle, which sucks air down the transmission tunnel; hence the Ferrari 355 belly pan with tunnel exists to the rear. Lastly, excess air that is not forced through the radiator is expelled over it (or under it in the case of a radiator leaned forward) like an airplane wing. Meaning, leaning a radiator forward may actually cause lift, leaning back may cause down force. My last argument is that if you were to attach a chin spoiler to your cobra which way would it lean to create down force? This of course is just my opinion. You have been a great help to me in the past. Thanks for the banter.
--Mike