Holy Christ dude! And I thought I might be able to finally contribute something to this :| Looks really good! If you are second guessing any measurements, I was thinking that both the metal neck rod and all of the screws have got to be standard. What measurements do they have now?
Haha! no worries, we're a long way from home, plenty of room for help.
The two measurements I have on the neck are .704" (side) and .745"(front). I consider the front view to be one of the best reference photos around (from the magazine cover with Lucas) because is it almost exactly straight on and it's taken with a high focal length lens (zoomed way in) and there is very little lens distortion. With those two measurements, I'd be comfortable calling it a .75" shaft. Also, It's a pneumatic cylinder shaft. I have one of a similar size at work I'll check tomorrow and I'll bet they match up.
As for the hardware, the face stuff is all pop rivets in the original Rex and those can vary in size but look what magic happened when I dropped in a 2-56 button head screw from McMaster:
I'd say we're within a tenth or two which is extremely exciting! It's been a long a frustrating measurement war and I'm glad to finally have things lining up.