Phil’s design is almost identical to mine, except that I’m CnC’ing the brackets and my boot is one piece. I also went with extrusion (though I went with 20x20, because it was left over when I converted from 500x500, to 1000 x 635).
Phil, have you checked the actual clearance between the V-wheels on the Z and the X-carriage V-wheel nuts? With the 20x20 extrusion, I’ve only got a whisper between them.