I recently purchased a 1968 Road Runner with the stock 383 and 4 speed trans. I've noticed that the factory dash tach is reading about 1K rpms too high at cruise. The car has the orange electronic box on the firewall so I'm assuming that it's some sort of electronic ignition. I don't recall my original Road Runner having this type ignition so I'm guessing this may have something to do with the tach input?? Any ideas?