Frank,
Just an added note from Pre '68 Dave's comment. Something else to consider on this topic might be the question "Are the engine/flywheel an original match set?".
My '51 currently still has the original 216 flywheel, but a later '54 235 my grandfather installed back in the early 80's.
When checking/setting timing in my case, I have had to ignore the existing "ball" marker and use my grandfathers added mark to get proper idle and performance.
