1) France - 6740 is the equivalent of our postcode and covers Châteauneuf-Grasse in Provence.
2) The record of the deed poll will be in registers held at the National Archives (Series J18) . There would be no new birth certificate - a deed poll doesn't change the name you were given at birth, just the one you choose to use from then onward. As an enrolled deed there should also be an announcement in the London Gazette.