Have thought about that, but going to stay in MPH as my Triumph's are also MPH. I grew up on the change over to metric so was always doing conversions for my parents at the time. I still think in Miles per Gallon and with the country travel I used to do, it was easier to work out an ETA averaging 60MPH, being a mile a minute, though up in North Queensland you would easily average 120KPH all day, so switched into metric mode, which was 10 KM in 5 minutes
The easiest way I can imagine changing to KPH would be take a picture of the speedo Photoshop it, print it and stick it over the existing face, a friend did this once on a VW Bettle he was doing up. I have seen the occasional Speedo on UK EBay with scales in MPH and KPH. I remember there used to be little step up gearboxes you could fit to the speedo drive, probably long gone, fine with a 120 MPH speedo but with ours once you pass what would become 80KPH you would be guessing.
I do recall having a conversation years ago with the guy who converted my VDO tacho for 4 to 8 cylinders. The speedo in my rally car was way out because of the low ratio diff and the gearbox from a car that ran 14" wheels, not the 13" that I had. He could recalibrate the speedo error if did some measurements like wheel diameter and distance covered in 10 rotations. Never bothered in that case, but we both may need to consider this due to the diff ratio changes and speedo drives on gearboxes totally unrelated to the speedo. Unfortunately that business closed up many years ago, but surely there will be others that can do the same.
I could have taken a picture of my speedo, but put it back together today. I chickened out in changing the odometer number drums. Came to the conclusion that if I made a mistake, broke or lost something I wasn't going to get another one too easily.
Just had a thought, Mini speedo's they were large diameter like ours and had the fuel gauge at the bottom. Had a quick search and found this. Ouch $350 for a brand new one!! No measurements given, suspect they are not quite as big as ours
Getting back to the electrics, I noticed my van has no voltage stabiliser that I have found so far, I think they are usually mounted on the back of the speedo and definitely nothing in the front loom I have removed. Wondering if this is because it had a generator and what effect an alternator will have on the original fuel gauge(the VDO gauges don't need one). Also while the speedo was apart realised the was no hi-beam or hand brake warning lights. Another thing that doesn't seem to exist is any cable or wire to the gearbox for reversing lights.
Fun fun fun. Checking out gauges on Ebay last night I found a VDO oil pressure gauge, which has a built in warning light. Both the gauge and light working off the same sender unit, designed for hot rods or where space or looks are an issue. I will be using this, so it will free up the original Oil warning light for something else.
Let me know what your sparky thinks if he doesn't run off screaming first.
Cheers Stephen