I have done 3 headliners, all three had front and rear glass still in it. I have 2 more headliners to do, it gets easier the more you do, but its never easy, thats for sure.I always leave screw in their holes, so you can find the holes easy, make an incision. I also like to clip the headliner tight, let it sit for a few days, then stretch it tighter before glueing. Complete process is around 10 hours I suppose. My buddy had a professional do his 67 GTO, that guy did it in about 4 hours, but he has done hundreds of them, and he used a steamer for the wrinkles. I have about 100 alligator clips, they work awesome.