If there are marks on the flywheel three inches away from the hole with no precise pointer then they are useless. Stupid design.
However, the way you describe your dad timing it is how I do it (with the Packards though they have an easy scale and pointer on the front vibration damper, plus an octane Vernier on the distributor) and is in my opinion a more accurate methodology for the specific fuel, engine and driving conditions for that car. So the markings provide an interesting baseline but aren't that useful anyway. The only proviso is that one must have good hearing for the drive test.