Did a search but nothing turned up. Maybe that means it's not a good idea. I've got my suspension blown apart to replace all the bushings and ball joints. I am going to do the reinforcement on the LCA and wondered if I should do same on the upper? A plate between the flange on each side and the inner body should stiffen it up? I saw some flex as I was removing the upper ball joint, but I was reefing on it pretty hard. What say you?

My understanding is that the UCA takes very little load so deflection is not a measureable issue. The "triangle" shape is inherently a strong one so the stock design is quite adequate. The tubular replacements offer only slightly less weight but are often built with more caster either built into them or attainable through adjustment.

I've thought about this too at one point, but the UCA sees way less forces than the LCA, which also needs to absorb braking forces.

Bracing a LCA is done quite often and I've done it myself too, but I do think the plate that is being used is way too much material and weight for the purpose.
IMO a fairly simple X-brace on the bottom should do the trick here.

But if I do wanted to brace an UCA, I would probably use a piece of 1/2" ø light tubing with a bend in the center so it touches the sides and the center part together.

Waste of time to reinforce the arms, unless you have some special application none of us here deal with. There is percentage wise so much more "Flex/give" in the suspension design, bushings etc that any reinforcement stiffness would never be even detectable, if even measurable, and the fact that the items never(?) fail, and when they do, in a contact situation, they sacrifice themselves for the sake of the unibody. My money however is on you at least adding the LCA plates, simply because everybody else does, but they also can't share a justifiable reason why, bang for buck, in that if it's just to be stronger, why not use 1/4" plate or thicker?

Speedbumps and roundabouts.
I think there are more of these things just in my hometown then there are in all of the USA

I do think a piece of railroad steel might just be a bit overkill to replace an LCA with.