Here's a how to guide to replacing the kph speedo face with an mph one.
I got the face from HERE
Removing the 70s imitation wood dash is a bit tricky - you need to remove the ingition key cover to gain access to the lower screw and the right hand fresh air face vent to access the other - that's the hidden one! The other 2 screws are obvious in the speedo cluster area. Be prepared for a few scratches when wiggling the "wood" out (ooo er missus
4 screws attach the speedo cluster to the dash, then separate the perspex outer from the cluster
At this point you could remove the offending buzzer relay, it's a push fit into the cluster. No more reversing buzzer trying to confuse my reversing beepers in the bumper!
Using 2 teaspoon handles, carefully prise off the needle by applying equal pressure to opposite sides, remove the 2 crosshead screws and replace the kph with the mph face. Remember to change over the needle stop (it's a tight push fit into the face - there's a hole in the new face for it.
Refit the perspex front panel and refit in the opposite order, remember to bring the hazard light switch cable out before refitting the speedo cluster
my only annoyance is the 120 mph partially showing - if I'd realised that I'd have used some black electrical tape to blank it off - not planning on doing 120mph, at least not til I install Marty's powerplant
The mph plate is designed for a Hiace Powervan but apart from that slight niggle, I'm chuffed!