Roof cracks

1968FormulaS340 said
If it's lead and the body seam is in good condition, you can leave the lead in there.

If you have corrosion in the seam and need to remove the lead you have several options but none of them are really good for you and you will want a respirator, not just a dust mask.

You can wire wheel, sand or grind it out. If you use heat like a small torch to flow and scrape it out you will need to remove that part of your headliner and interior or you will catch the car on fire.

In an area like that I would probably use something like this.
(But like I said. I would really need to see what you find once you get it cleaned up.)

http://www.autobodytoolmart.com/usc-all-metal-premium-aluminum-filled-auto-body-filler-p-14787.aspx
http://uschem.com/products/docs/TDS_ALL-METAL.pdf

I wouldn't wire wheel, sand, or grind ANY of that lead out. The last thing you need is millions of tiny lead particles to breathe. Strip the interior and use a torch. That's how it got in there to begin with, and its by far the easiest way to remove it. And if its not lead, a torch works spectacular to remove bondo as well. Falls right off after its heated. Just don't breathe those fumes either.

If it weren't cracked, I wouldn't mess with it. But if it is cracked (and it appears to be), then it needs to be removed or any bodywork over the top of it will be subject to cracking as well.

As far as the All-Metal goes, it would hold up a lot better than bondo. That's all I ever do body work with. Harder to sand, but it won't absorb moisture like bondo will. But I still wouldn't use it by itself for the roof seam. The All-Metal is a lot harder than lead, so, more likely to crack than lead would be.