I drilled the bolt hole, fastened the bolt (plate on backwards facing cab, bolt from behind) and drilled hole to install the rivet. I only installed the bottom rivet so the belt hid it.
[wuote=BurningTracks]
I wonder if the rivets are necessary reinforcement, or just to keep you from having to hold the back plate up again if you replace seatbelts in future.[/quote]
They are to keep them in place in case you need to remove them.
I'll likely plug weld the shoulder backup plate to the inner panel.
You’ll need to bend the plate to make sure it sits flat, as in the photo.
I took a different route with mounting them to the floor. I fabricated 1/4” steel plates and 2”x 3” angle iron mounts. I didn’t like the way the belts were routed over the edge of the seat frame, so I cut windows thru the back frame near the top which gave me a much straighter route.
