I would question the fuel economy figures that they claim for the 2CV. I've never owned one myself but know several people who did and they claimed high 40s mpg dropping to low 30s mpg if driven hard. I can easily better that with an 1100cc Peugeot 205.
I seen the wood burning idea before. It was used in French agriculture to power tractors during the second world war and was used to power buses in Thailand.