I just went through this with the 66. In my case, the division bar (vent glass side) has a separate vertical piece of rubber that gets riveted (4 rivets) to the division bar to complete the rubber triangle for the vent glass seal. Also the division bar is mounted to the chrome frame with two lower rivets and a screw at the top. Lastly, the top rubber seal has one large rivet to hold it in place. These rivets were all tubular type rivets from the factory. The top seal had a new tubular rivet supplied while the replacement division bar vertical seal came four small "forked end" (my term) rivets that seemed to me to have potential problems trying to install them. I found someplace to buy some small tubular rivets to substitute for the "forked" rivets but ended up not using them. Mustang vendors sell a tool ($75 - $90) that they claim can be used to install the rivets, but I couldn't see spending money on a tool that might not work on those "forked" rivets. I ended up making my own rivets out of small copper nails for the vertical division bar vent seal (threw the forked ones away) and used a combination of punches and drifts to form over the top seal tubular rivet. And, I replaced the two lower division bar rivet fasteners with small flat head brass bolts that I countersunk into the division bar/frame so the channel would remain unobstructed for the new window guides/felts.
66 Fastback
85 GT Hatchback
67 Coupe
82 GT Hatchback