Brakedwell and JW411: happy New Year (a bit late).
I can't comment on Hastings codes, as I only ever flew in one (Lyneham-Gibraltar, and that was a Met1).
But I have notes on some Beverleys: XL148 of 242OCU was "Y" and carried MOBCY, 53's XB268 was "D" MOBXD, and XB284 was "H" MOBXH. I flew from Abingdon to Odiham in "H" and then on to participate in the Farnborough show in 1961, thanks to pals at Abingdon.
I think I recall that the MOBxx code was painted quite small on the nose, and was also on the instrument panel. I had assumed that the B was type, the C or X was unit, and the last letter was the aircraft code.
Laurence