The OP's question was specific to the Dr Jig design, so I'll try to bring
this thread back on topic.
Like you, I've been looking at the Dr Jig design for a while. I really
like the clever double rail clamping system. Very simple and flexible.
It eliminates the need to use expensive C-clamps (which can slip)
or welding to the jig (which can warp it).
Unfortunately, the basic Dr Jig package is a bit too expensive for me.
But I think it can be DIY'd a lot cheaper. First, the doubled cross-rails
are unneeded. Second, I don't need the leveling legs, wheels, fancy
red paint, and stick-on logos. Third, the Dr Jig folks went to a lot of
trouble building those doubled rail supports so the bottom side of
each rail is unobstructed down the entire length. You can clamp
anywhere along the rails with their design. Clever and rather nice,
but I suspect I can get along fine and avoid clamping in those 3
little sections. Fourth, I suspect the 5 ft width is a smidge too wide
for the unibody cars I want to restore. The footprint should be well
inside the outer rockers so that the long side rails do not interfere
with body work.
So I plan to create my own chassis jig using doubled rails. But I'll
narrow it for early Mustangs and simplify it a bunch. Doubled long
rails using 2x4 tube. Three cross-rails using 3x4 tube. Ditch the
complex u-shaped brackets holding the long rails apart. Instead,
weld the long rails together on a piece of 1/4" plate. Weld legs
on the underside of the 1/4" plate. Done.
