Sorry I don't have measurements on the metal piece. It's not really that hard to measure/eyeball because that cupholder piece is removeable. So you can trial and error it (I got it on the first try).
I think more than actually telling you how to do it, it was meant to be an idea of what's possible. I hadn't seen anything like what I did yet, so I posted it.
Also everything is holding up great
Now that I have an armrest, not sure how/why it wasn't there to begin with. Makes it MUCH more enjoyable to drive long distances.