I don't have experience removing a hardboard headliner from a Duster, but I did pull one out of a mid-70s Dart in a junkyard, trimmed about 6 inches off its rear end, and put it in my Cuda (and it's still there today). There was nothing physically holding the headliner in place except the overhead light, visors, rear view mirror, clothes hangers, upper seat belt attachments, and interior trim. Remove those, and the headliner just falls down. When disassembling, I left the overhead light for last, since it's in the center and I figured it would hold the headliner up when everything else is removed – that worked well and allowed everything to be removed, and when I was ready to take the headliner out of the car, I just removed the light. If I remember right, I removed it out the passenger side, since there's no steering wheel to get in the way, and I had to kind of twist it around sideways to get it out.

My headliner is painted, and at one time I though about gluing some fabric to it also. But then I got a 5th Ave with a hardboard headliner and glued fabric (from the factory), and that glued fabric was always sagging down. That got me thinking that my painted headliner is just fine...