I thought of this many times. There is plenty of room under the headlight assemblies if you move a few things around.

I spoke with a well known s/c designer(Larry at Endyn) about this. He said water to air will be more consistant and the gains of switching to air to air wouldnt be more than the hassle/cost.

Still i think of this idea often. Hell i even have it designed in my head with special manifolds. Just not willing to be the first ginuea pig on this one. $$$.