Ding, Ding! Now I remember. I had the front and rear windows' weatherstrip replaced on my 66 Hardtop in 1996 or 97 at a local Mustang shop (it was going to be used as a daily driver). I had to remove the rear seat and package tray prior to the rear weatherstrip going in, but the shop wanted the package tray to finish off the job, which I brought in. They used the edges of a scraper to lift the weatherstrip over the package tray, not the sharp ends, and shoved it in. It didn't take long.
But it was all for naught. A couple of years later, I removed the package tray, covered it with the hide of the South American Nauga (aka Naugahyde, in black) on top of 1/2 inch thick foam rubber and installed a pair of 6 X 9 speakers.
It is still a daily driver, but looks sharp.
Jim