For those interested in the 2CV angle there is a test of the original car here
Citron 2CV6
It got 50.2 MPG with a 'touring speed' of 48 mph.
A lot of my 'if only I could build my own car' ideas for hypermiling have centred on the 2CV because of the seperate chassis makes it easy to put a new body on. With a bit of car I could see a car with a body closely matching the drag template shape and with 2 seats on there. There was another 'special' built in the 50s which used a 2CV as the basis - 4 wheels though - which was capable of 100+ mph on the long, straight french roads. Took a while to get there though.
Similar to this one, but I don't think it was this one as this is a panhard factory car:
I'm not so sold on the 3 wheel concept. They do have some exemptions here such as emissions testing and being taxed as a motorcycle, but there must be strong and valid reasons why the major manufacturers only make concept 3-wheelers and not volume production ones. 3 Wheelers with the 3rd wheel at the front always seem just wrong although I can see the point for aero - narrowest part into the airflow first.
I do recall a Morgan 3 wheeler with a 1930s motorbike engine at the front held the outright lap record at an English circuit in the 1980s at the same time as 500bhp+ Sierra Cosworths were racing at the same circuit.