Better to have the cardboard pieces too big than to small. I've got 4 out of 5 pieces installed in my '54 Suburban and the second from the front (you have to start at the rear) did not have enough material so it could be trimmed to fit properly (pieces one and two were OK and three needed to be trimmed a little). I have not gotten to number 5 (the front one that goes under the windshield rubber).
As you work from back to front (on Suburban or Pickup), the headliner bow goes over the cardboard (and thus there is no problem with fitting the rear piece to the bow). Also, the bow is screwed into factory holes, so each bow is a re-reference point for the next panel (the rear of a panel is pushed into the front of the bow).
Of course, a perfect fit at both back and front is needed on the front-most panel (its rear side goes into a bow and its front side goes under the window rubber).
Tim
