Easy to tell these blocks aren't factory even without the added M. These blocks have the 246330-M cast on the right side of the block instead of the left side like factory Hemi's. The wedge blocks also use the same casting number.

I've seen very few of that version.

This post is worth even less than the previous one, but I've attempted in the past to figure out the rough timeframe for this one change detail, given up and failed.

If someone goes digging for that info, I'm not your guy LOL.

When that happened, there should have been an upsuffix (the end of the part number would change to reflect the physical change, like AD to AE, etc),
but there is a good chance it was not documented in a way to provide any visibility.

I think the block casting numbers have been on both sides, some one side only (probably depending on what year and which foundries they were cast in)