Hello,
I also have an extra original VDO Mercedes Tack, out of a 6.3. These tacks are electronic and will not register correctly in a 6 cyl car.
I had one of these units re-calibrated to read correctly in a 6cyl. I used it in my W114 sedan rally car years ago. In addition I have some extra instrument cluster housings which you can use or practice modifying for the tack. Some slight modifications required. If your other options do not pan out contact me
ja17@att.net.
Where did you ever find a sister who would sand your car in 12 degrees no less!