The 36 Ford 5W Coupe with a fixed rear window has a track for the package tray from each quarter windows all around the back.
If there is a roll down rear window, then there was a track from each side of the rear window to each quarter window with a drain trough for the rear window with about 4 small tabs to support the package tray below the rear window.
Couple pictures of the metal package shelf supports which also show the vertical wood support midpoint between anchor point on the B pillar and anchor point at the edge of the rear window panel.
The actual support is an angle around the curve that transitions to a flat from the front of the shelf to the B pillar. The large flat piece that curves around the back in the first picture is panel board sitting on the support.