Change tachometer

Hello together,
I'd like to ask the electronic pros here.

My question is:
you can use the 200 20V tachometer
( red range from 7000 rpm )
Remodel from the speedometer disc and the scaling for the V8?
I'd leave the watch dead for now.
And then
I have the problem that my plus motor is turning more than 6600 rpm (beginning red range with V8).
That's not even the problem.Only my tachometer from 7200 stops completely and remains like a hit, but the engine turns in 5. The route is still easy to Tacho 265 (climate 254).
This means that the car still drives about 20 to 30 k/mh faster from the moment the rev indicator stops.
At ABH my limiter was anyway at 7200 rpm

Is there any way anyone can find a good solution?

Thanks in advance and all good things are Quattro.