Tachs pretty easy, takes 2 boxes I think. http://www.superturbodiesel.com/std/adding-a-tachometer-t-97.html

You need to swap your rear diff out. I recommend a 2.88, maybe even a 2.47 if you are up to snuff (and then some).

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
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#1995 E320 Touring
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OBK #42