[aerohead]

This won't help retro-wise, but the specifications might add some data points you could use in design:
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* 1997 Mercedes-Benz, F 300 research vehicle
* The only data will be found in the March, 1997, AUTOMOBILE Magazine, page- 10, by Georg Kacher.
* Cd 0.18
* Af approx. 21.891-sq-ft ( maximum ) [ the cabin is C-Class size ]
* 1760-pounds
* Length- 4495.8 mm
* 1.8-liter, I-4, Diesel TDI, 16-valve, cylinder deactivation at idle
* 110-bhp
* CVT transmission
* 110-mph top speed
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* If you GOOGLE the car, it will bring you back to EcoModder.com and an article I shared years ago
* The small photograph ( a single view ) makes body details difficult to discern.
* It looks like the upper grille is faux.
* Original wheel covers are missing?
* Rear skirts missing?
* Camouflaged non-aerodynamic features
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* My guess is that, 100-mpg occurred at around 50-mph ( the speed GM chose for their Ultralite 100-mpg figure )
* At 1/2-gallon diesel/ hour, the gross energy input is 3.55445-pounds/ hour, 68,387.615 Btu/ hour, and 26.86- gross chemical horsepower consumed, at the mpg-test velocity.
* From that, the thermal efficiency loss ( BSFC ) would have to be subtracted to arrive at the actual bhp.
* From the bhp, there'd be perhaps a 2.2% energy loss to engine accessories.
* Minus whatever the FWD CVT transaxle efficiency loss imposes.
* The remainder would be the Road Load horsepower, tractive-energy available at the mpg test velocity and test weight ( Mass ) to maintain velocity.
* It looks like the F 300 had about a half-rated power reserve, available for acceleration, and the car was speed-limited with final gearing.