So, why not weld panel between the two and connect them? So long as you don't warp either or both panels it would seem (no pun intended) that you could effectively eliminate this entire issue. Now, having said that, I understand why the seam is there, I understand if you ever had to replace the quarter (or roof) you would have to cut it all out (kind of moot when you think about it), and I understand that having laminated metal could be a great place for rust to form; however in my case with this specific vehicle, it is HIGHLY modified, not in anyway a restoration.
I completely understand using lead on restorations or even just rebuilding; I am not hating on it. I am discussing only my car in its current state which as I say is pretty far from original (4 link rear, lots of bracing throughout, 1.14" t bars, big sway bars, frenched marker lights, frenched rear quarter electric antenna, etc).
I also understand the issue of differing expansion and contraction rates of the roof and quarter, however it appears to me that if these two were joined completely (meaning fill the seam with a metal strip/panel) that this issue would be minimized.
for the record, my car will be Sublime when done. Oh and just for the record, I am not "scared" of learning to lead or anything of the sort, I am just trying to have an articulate discussion about the whys, hows, etc. This car has been an science experiment from the beginning; some might call it a rolling R&D project.