[aerohead]

I'm going to vote for 'b' also.And for the same reasons mentioned by Sven7.
The 'Spirit of Ecomodder.com' nose is like (b),with a bit of layback and is already producing induced drag (downforce).
FIAT research shows the same Cd for 'straight' and 'layback',so there's no apparent drag benefit to the layback.
The forward-projecting angled shelf or splitter would increase the induced drag,so unless you're going to track race the thing,there's no point.
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I would mention also,that if the distance from the nose, to the face of the radiator is less than the height of the radiator,then you might consider moving the nose forward to that dimension.
It will allow the minimum entry opening (if you do an airtight duct ),and also allow some plan curvature/radius which would help in crosswind drag reduction.