Took a 35 minute break before lunch and aimed the torch at the frozen brake line nuts. Worked like a charm.
I got both brake lines off, and I've been to the parts store for the right number of new lines, nuts & unions to reassemble it.
We'll still be using the flare tool to re-use the forwardmost section of the original lines (because that area wasn't corroded, and has a bunch of jigsaw bends & turns in it that would be hard to duplicate).
38 bucks later... it'll take a trunkload of recycled batteries to recoup the cost of this repair!