That's looking great Joe... can definitely see the designer in you coming through with that chunky funky machined bit!

The only thing I can raise is that I think Jazz commented that attaching supported rail to alu profile can be tricky depending on the spacing of the holes and the internal shape and thickness of the extrusion.... maybe you've already checked.... otherwise might be worthwhile checking with somebody who has seen both of these in the flesh so to speak.

I wouldn't worry about changing things completely again.... I'm starting to think that it may be better forever just re-designing in sketchup than ever building the wee beastie... Lol