HA! Jack, I feel for ya!
When I got my sliders the guy finished them 3 days before Moab, I had to scrounge to find a welder (I ended up using my muffler shop to do it on FRIDAY before I left!)

But, my standby was I had them bolted on Thursday. I had square plates welded to the posts that generally lined up with the frame contours - not easy. The plates had holes so I just jacked and propped the sliders into place and with a hammer drill I drilled into the frame with a 3/8" and then tapped the hole and bolted the skids on using lock washers. As an added security, on one hole at the front and back I went through and through and used a nylon nut on a 3" bolt.

The hard part is to prop them up in a position that won't end up shifting when you attach them, mine ended up a tad too close to the cladding at the front on the bolt up, we moved it 1/4" on the final welding.

So first off - do those square plates line up flush with your frame bolt on points?

If so, then pile up a 2x4 jig to hold the sliders square and steady as you drill the holes into the frame. Tap, bolt.
I recommend putting a long flat piece of narrow plywood between the slider and the lower cladding/frame just to make sure you have an even gap and you're not too close to the body for it to bend/vibrate into.

Once bolted on, I'm sure you can swing by somewhere in Moab to fully weld them on - if you're happy with the placement.

Good luck! I'm sure you can guilt the welder into doing it