Oil Pump cover plug types

Does anyone know what year Mopar went from a square plug to a hex plug on the oil pump covers? Typically no date codes on these and hardly nothing on the internet about this part of a restoration that I could find. Thanks,

No help here? Is this another part that is not fully addressed for a restoration?

Square at least through 1971. Not positive on the later years.

IV wondered this too once was told it a vendor thing and not a year change

Thank you. I do think year may be related. The casting changes and removal of PDCP is consistent in what I have seen on these. Looked at about 10 Square plugs and 5 hex.