If its the same one as I changed on my 1972 4/4 you should be able to remove the actual switch assembly by undoing a small screw and sliding it out with no need to remove the lock mechanism.
The switch assembly then slides out and is connected to the loom by ordinary bullet connectors.
The source for the switch is from a Vauxhall Chevette or Mk 1 Cavalier.
Hope this helps
Kind regards
Arwyn
