Yep its just painted steel. The steel ribs have a beaded welting on either side, much like fender welting or cowl welting as I remember. Last one of those was 30+ years ago.
Gee I'm getting old!
Somewhere along the line, my Bud Cab PU had headliner installed. I have threatened to take it out several times, just can't bring myself to do it, especially not knowing what's under (above) there.