I'm currently in the process of making a working replica of the OEM tachometer gauge for my Kadett C, using 3D-printed brackets to hold the guts of a generic 52mm tachometer in the original gauge cluster. I'm close to having a working prototype, Ill add a link to the 3D files when it's done if anyone's interested.
To get the gauge face looking authentic, I'm thinking of making a vector file to send to my local sign-maker to cut out vinyl stickers.
I've tried to recreate the gauge face (witch I believe is close to identical between the Kadett C, GT, Ascona/Manta) by photoshopping images of an original gauge, but due to my severely lacking skills in photo editing, I can't get it to look anywhere near right
To get the look authentic, I think the easiest and best solution is to get a scan of an original gauge face plate. The problem is that I have currently no way of getting my hands on one...
If anyone has a tachometer laying around, it would be greatly appreciated if you could provide a scan of the face plate.
If there's any interest, and if anyone is willing to provide detailed measurements I could try to make similar brackets for other gauge clusters as well, as these tachometers aren't exactly getting easier to get a hold of