The third row, by the seat of my pants. I copied from pictures, the angles and bend diameters from a non-correct year middle seat. I just widened it to be within so many inches of the upper corners and enough to clear the wheel wells. I'm happy with it and spent somewhere around $40 in materials. I could've done a little better with the sheet metal, but my mistakes are where most folks won't be looking. The lessons I learned made for a better job on the middle seat.
The middle seat, I copied a middle seat I had. I believe it was for a later year Suburban but I'm not sure which.
I also built both of them to use 3/4" plywood for backing, covered with 3" of foam, covered with the covering of my choice. I believe the foam and the Naugahyde was the most expensive of all the materials I bought.
