Holley Blackheart transmission Cross member
You are correct MoparMatt2000,
Here's a side by side comparison. Top pic is B Body. Although the center section is similar. the end section is different probably because floor pan between A and B body is different. Much longer spacing between bolt holes.
Holly does not show an A-Body Blackheart crossmember , probably because there is no demand for it. If it was an item there was a market for, I'm pretty sure they would make it.