As noted in this post, apparently C5AE 390 blocks were cast with crossbolt bosses similar to the '64 blocks. I haven't had much luck determining if it is all C5AE blocks or just some. If anyone knows the answer to this, I am all ears. 
Thanks in advance.
From what I’ve observed, it’s definitely not all C5AE-A blocks, only some. Certainly no where near as common as the ‘64 model year blocks. They might be the second most likely garden variety FE/FT block to have the cross bolt provisions though, from what I’ve seen. I try to watch & log casting date codes and other block characteristics I see, both in person and on the internet, but unfortunately not many people post all the details of their blocks, so I don’t have any definitive patterns yet. There were also two different & distinctive formats of how the “C5AE-A” block engineering number on the side of the block “looks”, but again no idea if there is any correlation between the “style” of engineering number and whether it might have the cross bolt provisions. Hopefully maybe some people will post up what they’ve found.
