Instead of using nutserts to hold the skid I decided to improve upon Jeep's design and insert 3/4" OD 0.109" wall DOM tubing through the frame with a weld washer on top so that a 1/2" bolt can slide through with a nut on the top side.
The first hole is centered on the rear bend, the middle is 9-15/16" in front of it, and the front is 7-15/16" in front of that one. They are positioned 1-1/4" in from the outside edge. My white marker went wherever markers go when they die, so you'll have to put up with the notes in blue:
To keep the spacing exactly the same on the top and bottom, I drilled one side, flipped and rotated the frame section in the vice without readjusting the vice position. Just a little trick!
Where the tube comes through on the bottom I beveled the 3/4" holes with a 1" bit so that it could be filled with the weld and ground flush.
I cut the 3/4" DOM tubing a little long at roughly 6" each. I cleaned off the mill scale by chucking them into the drill press and using a strip of sand paper on them.
Weld washers were Blaine's idea and made out of 1/4" plate with a 1-1/2" hole saw, a 3/4" drill bit for the center hole, and tapered with a 1" drill bit so there'd be an area to fill with the weld.
The tolerances ended up being so tight that the DOM tubing was a press fit into the holes on the frame. A Jeep version of wack-a-mole ensued.
Here they are after welding:
And after grinding and a shot of primer:
After copying the lines where the laser shown from the take off frame rail, and it's ready to go back in the Jeep!