[Bicycle Bob]

For a surface radiator, you might look at snowmobile parts. They are sized for an air flow containing powdered ice crystals, so you'd need several. You might also look at flattening out refrigerator freezer compartments. I presume the weight will be far under the usual for car tires - any leads on a lighter tire/wheel combo?

You are right to be concerned about the front suspension area - it can be responsible for tremendous amounts of drag. I think you will find that double A-arms with a tension member to the spring will give the lowest frontal area, but interference is still a problem. You could save some detailing on the streamlining by using a low-pivot swing axle. Given that the vehicle will understeer anyway, and the tires should be narrow, you might even cross the axles, as in the Ford pickup "twin I-beam" arrangement. You can use a single transverse leaf spring to provide both suspension and anti-roll, and because it is a spring, it does not suffer structurally by being slender enough to fit within the streamlined axles taking the moment loads.
A similar spring can be used as an upper or lower pair of A-arms, but you still need a third member for the shocks. In designing integrated spring/arms, it helps to keep the flexing area fairly close to where you'd otherwise have a pivot. John Cooper neglected that point when he used Fiat bits on his first Formula 3 cars, and got oscillations under hard cornering.