Nuts? No nuts? If you’re trying to remove the trim a old school can opener works great if you’re not trying to save it...but if you’re talking about the drip molding then you’ll want to strip the paint in the seam between it and the roof and then you’ll want to drill the spot welds mine had lead not sure if they all do if it does you’ll want to hear the lead up with a torch and use a hand held wire brush to clean it off as you heat it
I'm not sure if you just pull the back part of the drip rail loose and expect to push it back on. Once you get it loose you can pull the whole thing off in seconds. Back in the 80s, I "practiced" in junkyards first and was able to remove mine in about 30 seconds. But I had a shop put it back on with a new vinyl top.
That piece on the 69/70 Mustangs does indeed have fasteners. To access them, you have to remove the weatherstripping. It appears your weatherstripping has been removed, so I'm not sure why you can't get to the fasteners. As I recall, they're just tiny, sheet metal screws.