I replaced my roof rail weatherstripping this weekend. After wrestling with the passenger side, I wanted to document a proper how-to guide for the driver side, as most of what I found online pretty much amounted to "start at the front and press it in". There's a whole lot more to it than that, so here's a first-timer's guide to how to install your B-Body roof rail weatherstripping with clear instructions.
The old weatherstrip removes most easily from the rear, behind the quarter window; pull it up from there and move all the way to the front. The very front might be stuck in a bit, there shouldn't be any adhesive but maybe some rust might mean you have to tear it off from there.
The new weatherstrips are several inches too long, at least for a '70 Charger. Match up a new weatherstrip with the old one, and cut it off maybe a half inch longer than the one you pulled off.
For installing the new weatherstrip, all I used was fingers/thumbs and a plastic body panel tool like this:
If you look closely at the inside of the weatherstrip--note that there are obviously left and right sides--the front inside upper edge has a square notch in it. If you look closely at the metal channel where you need to install it, there's a square metal clip in there. That's where you will start, to line things up.
You see the metal clip on the left side of the channel above that upper screw:
While I was in here, I discovered the windshield corner trim retaining clip that I thought was missing; it's just not overtly visible as it's underneath the weatherstrip. I'd already bought new ones and installed the new one on the driver side, where the corner trim is raised up too much. Unfortunately it didn't make much difference, I will have to look into that at a later time.
Anyway, the way I found to get the weatherstrip seated properly, and it can be rather frustrating, is to seat in the bottom edge of the weatherstrip first, then press in some of the upper edge of weatherstrip with your thumbnail until you can carefully jam it all the way inside the metal trim channel with the plastic panel tool.
The whole A-pillar process will fight you because the upper areas of weatherstrip will want to fall back down until you get things firmly started. Just keep at it, an inch at a time, until you reach the upper corner. Once you have the weatherstrip tucked into the corner, the rest of it becomes much easier. Just tuck in the bottom edge first, then press in the upper edge with the tool. You can then run the tool back and forth between top and bottom edges and everything should smooth out. At the end of the quarter window, stuff the little extra bit of strip in the hole there and finish tucking in top & bottom edges.