I have a 70 up cover on my 67 273 Dart with bolt on timing mark. I can read timing on both sides of the engine BUT... The timing mark on the drivers side is NOT 90 deg off of the mark on the pass side AND you have to use a different plug NOT #1 to see the timing mark on the balancer from the drivers side. If you can see the timing mark on the pass side of the damper then I would assume they used a 273 318 damper on the 340 and a 70 up cover