brake master cylinder core [cast# on bottom is 2225541]

There is also a casting date on them.

The only numbers I can find are a 3 next to the Bendix Script,
MC Bottom.jpg

and an illegible number on the right side, which looks to be a date code tag attached to the mold, to be cast in.
MC Date Code.jpg

There are no numbers stamped on the left side, as shown on page 84 of the article.
MC Left Side.jpg

The lid has the pre-1970 lettering,
MC Lid.jpg

And the gasket has the number 2225441, which I think was originally published in the Mopar Action article as the casting number for the MC, and then re-published all over the Googlewebs, causing lots of confusion.
MC Lid Gasket.jpg