Yea, the cardboard ones do not fit very well. On my 53 I weighted the 2 pieces so the would somewhat flatten out for about a week. I then connected them correctly to the “S” shaped metal piece and duct taped the back side to keep them together. Just prior to installing I misted water /ammonia on the back side to make it more flexible. To install the whole headliner as a unit I had access to heavy packing cardboard corners and cut 2 of them to hold up the whole headliner against the roof but could still wiggle it around to position it for maximum coverage and least gaps. There is a good “Cardboard Headliner installation” in the Tech Tips. Link below that I followed. I was not satisfied with the cardboard (bows and moves because of our typical 99% humidity down here) and have already bought the 1 piece (not installed yet) and will have the same door panel upholstery glued to it.
Cardboard headliner install
