Here are MOST, I missed a couple in this shot, of the parts that make up the seats.

The rear edge of the seat back is attached to the seat bottom with a pair of narrow brass hinges. Then the rear of the seat bottom has an adjustable shelf pin attached to it that rides in the groove of the side support blocks.

The front of the seat bottom has a 1/2 inch conduit leg under it. Because we could not make tight radius with the conduit, we used copper tubing pieces to attach to the seat.