That German web link is for replacing a defective van tach internal mechanism with one from a VW car.The procedure for installing a VW tach into an 84 van that originally came with a big clock is much different.Simplest way is replacing the 84 clock cluster assembly with an 84/85 tach cluster assembly.It still takes some work. This has been covered here many times in the past.
Mark

    On Sunday, August 18, 2024 at 12:07:29 PM PDT, Vanagaudi <vanagaudi@gmx.de> wrote:  
 
 You may check for a tach out of a Volkswagen Golf Mk2, Jetta or similar
MJ 1983 – 1992. By some minor modification they will fit. On following
web site you find the details. Sorry, it's German language, auto
translator will help.

https://www.t3-pedia.de/index.php?title=Drehzahlmesser_Umbau_aus_Golf_II_f%C3%BCr_den_T3
https://en.wikipedia.org/wiki/Volkswagen_Golf_Mk2

On 18.08.2024 15:25, Eric Caron wrote:
> Sending again as I didn’t see this on list or in my junk.  I hope it reaches the list.
>
> Hi folks,
>
>          We just returned from a 10 day travel and camping adventure in our 84 Westfalia.
>
>          One thing I learned is that Heidi and my other drivers need a tach.  I would like to replace the broken clock with one.
>
> So, Tach anyone?
>
> Eric Caron