[Lynn Eades]

Your Engine cover side plates will be A.P.,at least on the left side, where you have no outer armour. The Bren plates are about 4mm down to the lower engine cover rails. I cant help withe the numbers except that I have observed dated bits (1938) that must have been in stock, that was at some point used in either new construction of, or the repair of a U.C. of post 1940 production.
How a plate was marked may well have varied from one manufacturer (of carriers) to another, in the U.K.

Are you able to make your photos any larger?
I will respond to your emails soon.
Lynn.