The lip OHMY34 is refering to is the metal lip that Ford used in attaching the original cloth insert into your original top. It will go completely around the perimeter of the opening. This may have already been cut away when the previous owner welded in the insert that is now in the car. You need to make several posts on forums such as Metal Meet Forums to get as much "how to" input before you start. This is going to be a major job. Plenty of welding. The location of the new opening and the fit of your new insert will have to be precise. Do you plan to do the fit up and welding yourself?