Looks like you've got him set up!
If your current tripod doesn't feel steady enough, or you need it back for your spotting scope, I'd give high praise to the Two Vets "The Ruck"- (
https://twovetssportinggoods.com/the-ruck/), which is rated to 30lbs. I've put my 16lb Chassis rifle in it with the center column fully extended so I can shoot standing (6'3), and it holds it well enough, but would be even more solid at 4'. Your clamp you purchased would screw right onto the tripod.
I've got a RRS Arca 30 Head for mine, and it has become my go to for glassing, as it holds any spotter extremely steady, regardless of wind. I've also got the Two Vets No Name V2 for work purposes, and can say that all of their products are top of the line. Maybe overkill for what you're looking to accomplish, especially with a relative short term injury. However, I know a coworker of mine who has gone all in on a good tripod and arca compatible head combo to allow their physically disabled kid to make ethical shots with the use of only one arm, and I think most folks would be surprised just how steady you can get off of a solid tripod/head in various positions.