Well, a VX would be appropriate, but take a look at the list here...
Automobile drag coefficient - Wikipedia, the free encyclopedia
Go for the smallest car with the lowest Cd. A Prius would be a good candidate if you can find one for cheap. The car for your motor gets 0.31 Cd. Pretty average, but with a small frontal area you'll be doing pretty well.
You could throw that D15 in whatever you want, given enough time and money. But IMO the ideal swaps would be to a second gen CRX or an EG. EK should take it well, too.
(I have no idea on the price of an engine)