Originally Posted by Globaliser

Indeed: according to what I can see it's currently planned to be operated by an aircraft that's similar to the "299 seat layout" configuration, ie the first of the 744 seat maps in the upper row on that BA page. There are some small variations between different aircraft even in the same sub-fleet, and that may be why you can see only as far back as row 53 on the MMB seat plan for your flight when the BA page shows rows 54 and 55 in the centre block too.