If you can Tig in a block, that’s awesome.
Otherwise, I would just use a thin piece of metal cut oversized to cover the heat cross over.
The am not to comfy & cozy with a lot of JB weld in a spot that could be troublesome. Perhaps, maybe an epoxy, maybe. It’s just such a large area. I’m not fully aware of the ability of anything to cover that much area and have confidence over the long haul.