I use those same HF clamps on my table. but I was milling out the printer panels last night and figured out he holes are a bit too far apart might need some extra ones. Other than that it works great, and the top of those clamps are a little less than an inch tall I think.
Barry that was a very ambitious design to plot, looks awesome too bad it didn’t finish. I love your work space, man I am super jealous of that.
As for that coupler the next one you put on there put it on so it touches the bearing in the z mount, kinda trapped in there, should relieve the vertical stresses on it.