MAJOR PROGRESS!!
I realize we have gotten a bit off-topic but that is sometimes fun 
My Portable MPCNC Primo is built and moving!!
I had a much tougher time getting the thing all square than most of you because I have the legs going into tight-fitting holes in the torsion box, so I can’t shift them easily. I did have to shift one, due to a wandering drill bit. That was tricky! You can see all the latest photos of my build here:
https://photos.app.goo.gl/y33gZrdvMpYLSGuq5
[You can read the captions in the Info Window for each image, accessed by clicking on the i with a circle around it.]
It pretty much worked the first time!
I only had to edit and re-flash the firmware in order to get the logic of the Hall Effect switch endstops right. They are normally high, and go low when the magnet is near. I thought that is the same as what the mechanical microswitches do with C grounded and NC connected to a pulled-up signal line. Anyway, dual-endstop homing is working great. I have not done any drawings or racking adjustments yet.
First, I need to re-build the Z axis to accommodate my large spindle (65mm). The Makita mounts with the recommended holes set it way too low, eliminating most of my Z travel. I have re-drilled higher holes. And I am going to use two of the lower Makita mounts because the upper clamp gets in the way of its own screw holes.
At every turn I see clever design features. Thanks to Ryan and all of you who helped refine this design.