We imported our MGB in about 2008, so things may have changed. We registered it as a Voiture de Collection. The purchase receipt proved we owed no taxes, we handed over the UK registration document and paid the fees, then had to have an initial test at the local testing station who said there was no need to change the headlights as the car was authentic! We didn't have to have a Cert of conformity, owing to the car's age.
Ask your Prefecture to check the rules for Voitures de Collection. We were given a book of vouchers to complete if we took the car out of the Départment, not sure if that still applies, however it is a fair weather car and doesn't go far. Phil is too tall to drive it with the roof up!