I would advise anyone if possible to register their vehicles (especially bikes) in france. for cars MOT's then last two years, there is no mot for bikes. There is no road tax for either.
I pay 86 euros a year insurance for my bmw 1985 r80rt, third party only with medical cover for me and pillion.
before you embark on this route, go to a french insurance company Maaf are good, avoid axa and especially AGF like the plague. get to look at the -exact- model numbers they insure, and get one of those ( or have your 'export certificate display that model number). if it is listed bringing it into France will be easy. If it is not listed, it will be very difficult, plus awkward to insure.