the Manx Museum library (now open Weds to Sat only) has a copy of all the IoMFHSoc MI transcriptions - these books contain a plan of the yard - if you don't get a reply then this would seem a good place to go prior to revisiting the yard.

There are no such surviving (assuming if they ever existed) records for the old Braddan yard - parts of the new Braddan yard should be documented at the Manx Museum.