There is one real easy way to tell if the Tach is Original or a "Customer Addition"! The location of the cuttout! This has to be placed in a very Specific Spot! If you do not the base of the Tach will impact on the Master Cylinder. Then there is usually the early 69 Style Master Cylinder that was installed by the Factory on Early Production Cars. I never liked that Big Coffin style Master Cylinder!
