Flywheel surfaced - is there a thickness concern?

With 50 year old flywheels, unless you bought the car new, no telling how many times it has been resurfaced and how much. If it is severely heat checked, it may be relegated to boat anchor duty. It should only be resurfaced the minimum required to ttue it up. Preferably by grinding, not turning.
The working surface of the flywheel is actually raised above the rest of the casting. There is a height difference you can see. A quick visual check would be to see how much the working surface is above the casting. I think I'd like to see about 1/16". If the 2 surfaces are on the same plane, game over.