Just went through this myself. Assuming you have a standard 49 pickup, there was a change to the headliner during the year. Up to mid year, the headliner used a screw in channel in the center. Sound like that's what you have. The front is held in place by the trim around the windshield. The rear uses another screw in channel much like the one in the middle. Late 49's changed to a floating style center support. I have a late 49 but found out the hard way that my cab had the earlier style headliner. I ended up buying two headliners before I got it worked out.