Install the headliner in the car, stretching as tight as possible , (without tearing it), when you are finished, steam the wrinkles out, if you don't have a steamer, use a spray bottle, sprinkle water on headliner, close up car, let set in hot sun. The headliner will actually shrink, assuming it is cloth. Even some vinyls will shink. The header is cover with a panel covered in same material as headliner., and yes, coachlace hides seam at bottom edge of headliner.
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John