Just an FYI that some of these have no reference-able casting numbers.
The one I have has a "blank" set of empty squares that look like a casting number should be there and another number that is not the correct format and doesn't match any documentation I've ever seen.
It's aluminum with a terrible casting mark about a 1/3 from the left (looking from the rear) all the way from top to bottom.
I passed on several like this thinking it was a serious flaw until I saw the 5th or 6th one with the identical mark.