Body solder or ???

Heyo. I'm at the point with my Dart where I have to decide something. I've gone right down to the bare metal on it where the roof welds to the body. Two spots on the a-pillars and two on the rear sail panels next to the rear window. The 4 weld seams were filled with a body filler from the factory rather than being leaded. I've cleaned out all the old filler and now have to refill the seams which are fairly deep. Body solder (leading) is one option. However, I had an idea and need opinions.
There is a product from various manufacturers like LPS, Devcon etc. Basically what it is, is a two part steel epoxy, usually a tubular stick, one part surrounding the other. When mixed (kneaded) together it forms a super strong repair that is waterproof, sandable, paintable, can be drilled or tapped and is permanent. Very much akin to something like JB weld. Would this be a good alternative to body solder? I really don't want to refill the seams with a regular body filler. All opinions are welcome and thanks in advance.