Regarding your tach, it should be a 6500 rpm redline unit if it is original to the car. They a pretty rare. If it is original and not a 6500 rpm unit, it probably is meant for a V8 (in which case it will read incorrect). I know they make 6 cyl repos for the 68/69 models (low tach style) but the only repos I have seen for the high tachs are for the V8s. Bottom line, need to know what type you have first.