I'm looking to add a shoulder belt in my truck but keep it all original mopar as car as belts go. I feel like in the past I've seen what looks like a threaded nut attached in the upper corners of the cab where the shoulder belt bolt would go. Is this something you can add to a truck that doesn't have it? I'm not quite sure how it attaches and whether it needs welding or not. Thanks.

You can make a nut plate or find and old cab and cut that area out. Prep the nut plate, drill a big hole and a couple smaller. Feed the nut plate up the pillar and tack weld it in place through the small holes. Grind smooth and refinish. You need the re-in forcing nut plate to make the upper mount secure.

I too would like to do this. My cab has the holes already punched with a small cap in them from the factory. But as said above there is no threaded insert installed.
I have thought about making an extra large threaded backing plate and a large washer on the inside with a shoulder bolt to clamp the interior sheet metal. I'm sure welding it in would be best but i didn't want to paint the interior cab metal. Also thought maybe some type of panel bond on the backing plate....
Anyone else have any ideas??

I have installed shoulder belts in a lot of cars & trucks that didn't have any before. I usually start with a 1/8" thick, by 1" wide, and about 4" long flat stock. This plate will be mounted inside the door post, so adjustments will need to be made to accommodate the vehicle, but the size above has been proven to be effective. Drill a 9/16" hole in the center of the flat stock plate, then weld a 1/2" nut to the back side of the plate so a bolt will thread into the nut through the plate (a good heavy spot weld on every other flat is enough weld unless you intend on really cranking down on the bolt for some reason). If a hole exists in the door posts, use the existing hole,(factory holes are usually about 5/8"). If there are no holes present and I have to drill, I will drill fresh holes 9/16". The hole needs to be centered so the 1" bar can slide behind it and plate sits flat against the inside surface. Sometimes you need to trim the 1/8" plate, don't remove any more then what needs to be removed. The ideal location for the hole is slightly behind the seat back, just above shoulder height. If you do not want to weld the plate into the door post, you can drill it and add one or two small self tapping screws (one at the top of the plate and one at the bottom of the plate). The 1/8" plate really should be attached to the inside of the door post by screws or tack welded into place.

To hold the seat belt in place, I use a 1/2" grade 8 bolt,(same thread as the nut you are using) 1 1/4" or 1 1/2" long (there should be about a 1/4" to 1/2" shank left on the bolt beyond the threads). Add a grade 8 flat washer. When installed, the bolt should bottom out on the threads before it tightens against the belt end. If it tightens against the belt, get the next longer bolt. I usually tighten the bolt against the shank so it is tight, if your in doubt, you can always add a little Lock Tight to the bolt.

For this to fail, the 1/8" plate has to be pulled through the 9/19" hole, or pulled through the door post, or the grade 8 bolt has to fail. If either of these things happen, you would have been so screwed without the belt anyway.

For the record, I have seen this setup distort the door post, the rocker, and roof panel and not fail. It just about pulled the door post out of the car. I have used this setup in everything I have built in the last 10 years. I've seen it work, and I know it work. Gene