I don't WANT a higher peak, just a new tach. It's a 601 engine. The question isn't what I want but whether a tach which indicates 7000, with an arc the same as the 6000, would be accurate as a replacement, and with which face? I'm guessing the new tach with the old face with the same arc as the 7000 face, would be accurate.

I don't know what controls the swing of the needle and whether there is some restriction or modulation in the head units. The tach is out of a '91 gasser but I don't believe the source has any bearing on the question.