Mine was a total pain to install. I purchased one from Jim Carters back in 2000, you had to soak the corners in vinegar if I remember correctly then bend them over something about the same radius. Once bent you quickly shoved it up into the cab and secured it. It didn't work at all! I couldn't get it bent with out tearing. I then went to the local upholstery warehouse and bought three sheets of the same type of headliner for about 1/2 what I paid for the first one. I figured one out of three I could get into place. It took two of the three and that one I cut slot in the rear corners. Its not 100%, but I am happy with it.
The sides are held in with the same trim that holds the door seals ( the piece shown in your first picture with the screws in it ). The front and back have flat sheet metal trim that hold the liner in place. The trim pieces follow the indention or recess in the front and rear pieces. I will get you a picture of mine, its nothing fancy, just flat sheet metal with some holes in it.
