Anyway, from my understanding of cantilever beams, my plates should be strong enough. ......... As long as you get those correct, and the plates are parallel, the clamp should work.
Okay, so let me go back with something more blunt.
NO clamp is "strong enough". Never has a clamp been made that someone hasn't overtorqued or overloaded to the point of irreparable distortion.
You're obviously going for the aesthetics or you'd be using a different material. Building tooling from scrap is time honored. Building tooling from junk scrap is not.
I'm totally loving the aesthetic. I may pursue a similar pair. So you're that much of a trendsetter. You sold me.
Now sure, i might not use them to hold die shoes tight, but hey, the proper tool for the proper job, eh? These were certainly never intended to replace a (single) $50 Kant Twist in performance - at least I hope not. I just think once you get them drilled and the swivel faces made, they'll be an excellent addition to your tool rack and you, being a craftsman, instinctively understand their limits.
And (again were they mine) being hammered out, you could concoct ancient tales of derring-do surrounding these clamps that old Zeke the pioneer carried across the prairie - or somesuch shop talk for its entertainment value.
If it ain't fun, it ain't worth it.