If you speak to Tippers Vintage and Classic plates, they might be able to bend the plates for you on manufacture, to fit your 2cv. As all their plates are specialist I don't see why they wouldn't be able to.
As for being road legal on an '85, I think they probably would be. They wouldn't be period, but they should be road legal. In the 80's, cars went over from metal plates with plastic numbers to aluminium pressed plates.
All of the different styles are on their website.
New sports coil arrived today for my 126. Can't imagine it makes any difference to a 'normal' one, but it was the same price. Also now my 126 is insured on a classic car policy and it was dirt cheap! So much so, when it is running I might get rid of my other car!
Tom