2 X'S and an R

So I could not believe these are all in my garage at the same time, not all mine but I think I should buy a lottery ticket anyway!!!View attachment 1715722268

Can you give any more details on these blocks? What kind of builds were they used for, and what are they going to be used for? Just curious as we don't get many posts on these.
Looks like the X block on the right may have a four bolt main cap peaking out on the number two main.
The X block on the left has an extra bolt hole down toward the main journals. Is that for a gear drive?

Also looks like a Speedmaster box sitting on the floor toward the top of the picture. I assume that is not related to the desirable blocks you have there.