Here's the caster with black dots marked, where is where two bolts pass through to mount into the foot structure.
The kicker is one side is in a great spot, the other is a tad too close to the rounded surface.
I drilled out the mounting holes and pass thru holes....
Picture out of sequence here, but here you can see the one bolt (pass thru into the mount structure) that rides into the curve of the caster. As best I can figure, I'll just have to make sure this bolt is the last be to tightened up. Oterwise, it will throw off the alignment of the other screws.
So with that part sort of "settled" I found another small issue. But before confronting that, I wanted to be sure the 1/2 inch bolts would be long enough, with a lockwasher and nut. They are. I could upsize to a longer bolt, but I think this works fine.
...and alas the last remaining issue. I can't fit the last bolt to mount the caster into the plate. But honestly, with the other three holding it tight, plus the two pass thrus holding it, I don't think it will be a real problem from a strength perspective.
With this first one done, I'm certainly going to play and fidget more with the hole alignment. And gawk at the picture of Jerry C's setup some more.