The Brooks do run small for the tag size. I think mines a 42 or even 44 and its trim.
Having owned (still own) a Brooks and having had more Aero BR and CR than I care to count they are just VERY different despite looking similar.
Honestly, if you like the Brooks, buy a Brooks. You'll save a fortune and have the authentic thing. Part of the charm of them is the light weight leather and the fact they are all broken in. The only leather from a high end maker that even comes close is Eastmans Italian but even that is a bit thicker and stiffer. Aeros Vicenza, while lovely, will never emulate the Brooks leather, its way too thick and will sit completely differently on you.
Brooks is still in business and making new jackets....if you want new, why not try them?
A bit late, sorry. I hope still helps.
Back: 24.5 with a 1.5 front drop.
It’s a pretty cool vintage piece but I’m keen to let it go, so yours if you want it for what I paid, it’s a bit tight on my beer belly.