Sending units are usually date-stamped, Month/Year, like 'L5'
The 64.5 style warning light sender is the big stepped version, black. Later, maybe when alternator systems first started being installed is the small slide-on, olive drab. I'm sure there are variants of the small style.
For 66, have mainly seen 'KS' in script oval stamped at the top with a pressure rating, like '80' at the base and date code.