[Lugnutz65]

Originally Posted by DaddyOh

Is the shoulder anchor just a boss welded to the cab's sheet metal, or something more stout?

There is a large washer and nut behind the cab wall that gives the shoulder anchor the strength it needs to be safe. I welded the nut to the large washer and slid it up the B pillar with the string and nail you see in the photos. When I was satisfied that I had it lined up with the 1/2" hole, I tack welded the washer through one of the 3 small holes. It must be exactly centered or the bolt threads will catch the sheet metal and the end of the bolt will push the nut away and pop the spot weld. Believe me, I know.

Once satisfied the nut is centered, finish by welding the other 2 small holes. I'm planning to post a DIY thread on my website very soon. It will have all the measurements plus some tips.

One of the tips is to drill matching holes in the washer and then plug weld the washer in place. The weld will be stronger. Either way will work if the weld is done properly.