Get yourself an SB100 (I think that's California's name for it) permit/waiver/thingie that allows 500 Californians a year to build their own cars without smogging them...provided they resemble pre-smog automobiles. Then make a "replica" (the quotation marks are for the loose interpretation of the word) of a late '50s Le Mans racer.
Seriously, it's not that hard. To hit your target numbers I think it'll be considerably easier to start from scratch that to modify an existing car.
Click here...
http://ecomodder.com/forum/showthrea...-11009-19.html
...for my own Lola Mk1 inspired Locost rebody (I have the molds if you want parts) and the next few pages on that thread have some Lotus 11 pix.
The small displacement sports racers of the era were quite efficient; considerably moreso than their modern counterparts (which trade streamlining for downforce).