Concorde 44.18m, Alliance 46m--if memory serves European deck measurement is including the posts while American "between perps" is inside them. Not sure how much the posts add--though I'd suggest +/- tolerance of differences should grow and shrink proportionally to ship size. Ten feet is one port--enough to make Alliance a monster relative to her "New England Group" relatives, while considerably less noticeable comparing 74 Ildefonso to 80 Neptuno and barely a blip when you cut a one-port "slice" out of 120 FNS Ocean to make 110 Commerce de Paris or splice one into 100 HMS Royal Sovereign to make 110 HMS Ville de Paris. I'd need to find a good scan of NMM J5325 (Concorde as taken) and set it up side by side with the Alliance drawing to say better.

Drawings are from a scan from Millar, to give credit where credit is due. Bear in mind, many of Millar's drawings are what we might call "forensic reconstructions"--his best guesses based on similar known works at close to the same combination of time, place, designer, builder and size/role. I really wish we could get Silverstone and Millar to get heads together with each other and Winfield to pop out an "American Warships in the Age of Sail"...