I don't think it would be that hard to build a Mopar block. If BBM can produce FE blocks then they can do Mopar blocks. The blocks are roughly the same in many ways. Deck height, cross bolted mains, etc. I just don't think there is any magic involved.
If I was willing to invest the money (which I'm not) I'd just go visit BBM and talk to them about what it would take to do a Mopar block. I wouldn't do anything tricky, just a reproduction RB block that is thicker and stronger with cross bolted mains.
There are also Cleveland blocks being made.... I have no idea how many they'd sell but I dont imagine them being a high volume seller, even because in part blocks already exist for SBF - many cleveland builds are just based on windsor blocks that dart and world make.
And they are available in cast iron apparently, as well as CGI, and aluminum. I assume the same foundry handles all three castings.
http://www.tmeyerinc.com/product/track-boss-cleveland-block/Here are some pics of the cleveland and the foundry that casts them.
This aussie A body won best of show at the biggest annual mopar show with a HP Performance built Gen2 Hemi using the HP block, so when it comes to alu there is also HP along with the others that everyone here knows about.
https://www.whichcar.com.au/features/hemi-powered-chrysler-vg-valiant-hardtop
