My 70 Charger needed rust repair in the rear window area. When it was time to set the window back in place, I bought a roll of the butyl rubber "rope" in the 3/8 thickness. The channel was a little uneven from the repairs, so after I set the rear window, I went around the entire perimeter with the gooey black windshield sealant. ZERO leaks!
Regarding the trim clips, Its hard to locate their positions with the trim in place as mine are. A general rule on the A body cars was that the clips are within 3 inches of the ends of each piece of trim and often no more that 12 inches apart. I would imagine that the B body cars would be similar.