Hello.
Welcome to the forum.
Unfortunately I don't have any information about the Mercedes dashboard you would like to use to I can't really help.
In general you need one rev burner for the rev counter and one rev burner for the speedometer, plus a 12V power supply.
if you don't have the schematics of the dashboard my suggestion is to use an aftermarket rev counter that you can find on Ebay or many other websites.
Cheers
Cristiano