I found a build sheet under the rear seat. I had the seat out a few times over the years and didn't see it. After reading that it could be there, I removed the seat and found it tucked up under the springs and behind the cardboard sound deadener.

I dread removing that rear seat. A couple times I used towels to protect the front and rear seats then put plywood and 2x4 pieces in place and a 2x4 lever to push the seat back and out of the floor brackets.