Speedway, 35/36 roadsters did not have adjustable seats. The bottom seat frame sat on a wooden frame as shown below. It was trimmed as shown below. In the front corners of the frame were 2 metal pins that stuck up and fitted into a hole in each front corner of the seat bottom. You could remove the seat bottom and store tools etc. underneath, but no seat adjustment. The seat back frame was fixed in place and could not lift up like in a coupe. The gap between the seat bottom frame and seat back was filled with a metal plate(again shown below.
Hope this helps a little.
Don