[Walt Fricke]

When I put a 3.0 into my '77 Euro 2.7, I was advised to change my tachometer. The earlier tachs got their signal from the distributor points. When the points went away, the six pin CD box had a dedicated (and cleaned up) tach output - a pretty clean 12V square wave. This supposedly would not work with the original tach, and an SC tach was what was recommended (which I did).

But you have an even earlier tach, so this doesn't quite make sense. My suspicion is that you can't easily convert these by changing some passive electronic components inside the tach, but maybe you (a knowledgeable shop) can?