I have a '70 Z28 with the factory tach that reads about 30% low (compared to a known good hand held tach). It has an MSD HEI distributor and the fusible-link resistor wire has been removed. Does any one know of a reliable place that can recalibrate it? I'm in the south-east part of Wisconsin and would like to find some body in the area if possible. If not I guess I'll have to ship it.