Hi Bill...the change from a FLAT boss to the STEPPED style occured in October 42 and if the motor had a FLAT boss that would probably mean the number was 64582 because by 84582 they would definitely be using the STEPPED style at Ford.
I believe the order is something like this:
Flat boss, date wheel
Stepped boss, date wheel
Stepped boss, cast in (under dizzy) date....but the date wheel kept and the date not changed
Stepped boss, cast in date, no date wheel
Based on observations and what Tom W. has discovered.
GPW 17963 4/24/42 Chester, PA. USA 20113232 (est.)
GPW 85976 12/9/42 Louisville, KY. USA unknown
GPW 108552 4/21/43 Louisville, KY. USA 20371278
Bantam T3 4582 10/29/42 USA 0173499 (est.)