mpc; if you enlarge the pics you will see what looks like a seam along and about 1" above the metal window trim. That is the edge of the poster board I borrowed from my kids, they used a lot of it for school projects. It's dense cardboard, and can only be cut with a utility knife, scissors won't work. The only reason I knew what to do here is one side of the old headliner had these fabric covered pieces in place along tne metal trim, just stuck in before the screws were totally tightened. I copied the shapes, but they really just follow the metal trim contours, and are slightly larger to fit behind and still show outside of the trim. I guess you could make one long piece, but my kids poster board was only 24x30. I glued the fabric on with spray contact cement. These are cosmetic and do not hold the headliner in place.
The cool part of the tweed fabric is that it stretches in two directions, making the wrinkles at the corners go away easier. If you put the bows up you will find that the spacing at the front and back bows is wider in the middle of the roof, narrower at the corners. My wife sewed the loops for the headliner bows with this variation in width of the end panels, with the headliner layed on a flat surface. If you don't, you will have a fold in the corners.
The thing no one has mentioned is stapling the headliner in place. Replace any wood strips that won't hold a staple or you will have the thing falling out on you.
Hope this is helpful,
Gary