Engine ID code 10,000 day calendar vs month/day

My 340 purchase motor has a code "3" on the oil pan rail, so I assume it was used in a 1973 vehicle.

Per Page INF-8 of the 1973 Passenger Car Parts Catalog the year 1973 is coded as a "J" and the build date code used is the 10,000 day calendar. (i.e. 4136 = 11/23/72)

Per Page INF-8 of the 1974 Passenger Car Parts Catalog the year 1974 is coded as a "4" and the build date code used is the month day calendar. (i.e. 0910 = Sept 10)

It looks like the coding on the front of my "1973" 340 block is:
(first character unreadable 3? J?) followed by M340 04238299
0423 cannot be a 10,000 day calendar date. Maybe I misread the block numbers (see fotos).

I was wondering what codes other Mopar owners have found on their 1973 year vehicle small blocks? Do you have a "J" or a "3"? Do you have a 10,000 day calendar code or month/day? Thank you.

73 engine ID.png

74 engine ID.png

my 340 ID.JPG

DSC00098.JPG