A bit of a long shot, but could you get a cheap Tim tachometer or similar and swap the guts over. Only issue might be calibration so you would need one with a similar scale. I converted an old smiths clock like that, but obviously a time clock doesn't need calibrating, one revolution is always 12 hours! Or just buy a cheap tachometer and fit that.......
I have seen something about doing that and I think if I could get a gauge at the right price I would give it a go, the only problem is that I don't want to buy a gauge that doesn't work, I don't like buying second hand electrical as I know ho stupid people can be.
Good advice and I will give that a go, I never thought about using a cheaper tim gauge I was looking a smiths and they're a little more costly. I will see what I can get and hope that I will able to get the beautiful gauge up and running.