By now everyone knows that the rotary door lock that is mounted in the door is from a TR4, these are unobtainable new but can be found second hand.

They are also  fitted to the DB4 to DB6 as is & need no modification's, however if fitted to a MkIII the internal locking mechanism works the wrong way round, IE push the internal handle forward to open the door when you should pull the handle backwards to open the door & forwards to lock the door from the inside.

This simple kit replaces the part that is different & makes the rotary lock work the correct way round, comes with plate & new rivet which is easy to install.