I do not check advance any more.
If you have a vacuum gauge, attach it to the vacuum port on the intake manifold and rotate distributor to maximum vacuum (at idle speed). I think that some people then "back off" the distributor (turn counter-clockwise a few degrees).
"I know that TDC is the suggested advance on a 1957 235 (mine's a car), . . "
You probably mean the timing mark on the flywheel, rather than TDC?
Is that from the car Shop Manual?
