Welcome aboard, Gene.
You know a great deal about your Chiefs Special. Kudos.
S&W issued the order to stop using the diamond grips in
October 1965, but I've seen them used -- with matching serial
numbers -- through June '68. That thumbpiece began, again,
in about 1966.
Two examples on my list that bracket your serial number are:
556J34, which shipped in December 1972
&
593J24, which shipped in February 1973
S&W didn't ship in serial number order so yours certainly could
have shipped before, after, or in between those two.
Truth be known, I actually prefer the ones with a bit of character,
and square butts are my favorites. Looks as though someone
bobbed off the coarse portion of the hammer, too.
Enjoy it.