The top is riveted around the back window. You will need to drill out the rivets and then either weld or fill the holes. Don't use regular Bondo!!! It absorbs water like a sponge and will cause rust if used in an application where the back of it is not painted over. I used US Chemicals brand Allmetal as my filler. It is designed to replace lead as a seam filler ( GM used lead on plain roof cars to fill the seams). The other option is something like Marglass , Kitty Hair or Bondoglass which are fillers designed for fiberglass repair.Try not to use Tiger Hair which is a long strand filler and harder to work with. I always use one of these products as my first filler layer in anything where it needs to be waterproof, like the first layer of filler over a welded in rust patch or sectioning job.Remember that plain Bondo is not good in thicknesses in excess of .125 to .25 in as it has significant shrinkage and will crack and fall out over time.To remove the studs, clamp on to them with vise grips and twist them off rotating them parallel to the surface CAREFULLY! If not , you will warp the roof, and a G body roof is almost impossible to work on due to it's low crown. Try to use a grinder as little as possible since it will impart heat to the area being worked and can warp the roof. If it does, you will NEVER get it perfectly straight again. Don't ask me how I know... Years of a Domino's sign on the roof of my Cutlass made it impossible to get right again, even with 2 weeks of effort put into it.As for the trim pieces, the quarter windows ARE different between the 2 roofs, but the plain roof windows do bolt in as long as you use some butyl ribbon to seal them to the body.The plain roof quarter windows have a rubber seal that extends beyond the chrome trim instead of terminating underneath the trim. The rear window trim is held in by clips which are not present on vinyl roof cars. To install mine, I did the following: With the back window removed, I drilled holes around the window channel using the trim clips to help locate the holes. Then, I used some 3M window sealant in each of the small holes and screwed small stainless steel screws into the body. The panel between the window and trunk will require some different clips to install the trim. They are grey, not white nylon like the windshield/backlite clips needed for the other 3 trim pieces.I grabbed mine when I grabbed the trim and panel from a junkyard donor car.