I just did my 68 last week. Keep the headliner rods in the correct order. Start tacking the front or back first.Make sure the is enough material overhanging on all sides.In the center of your roof there are adjusting slots the rods slide back to front,which ever end you start from make sure you have room in those slots to pull the material that direction,it keeps the material tight from rod to rod. Contact cement works well for the adhesion part but the 3M spray adhesive sets quicker and is easier to work but it's 15$ a can.
The only thing diappointing about mine was the material still has creases from it be folded up in a box so long.I could not pull it tight enough for them to disappear,im hoping they relax over time.