Very nice detail work Andy, and yes, I believe that 'hatch' is for the drift sight, the 'head' of which is a periscopic lens barrel which would protrude beyond the side of the fuselage by a couple of inches or so.
I'd heard somewhere, some time ago, that Tamiya used an ex-Portugese Beau as the pattern, but I believe the RAFM example was brought back from Portugal, so it could be that one.