Thanks, velonomad.

As I think about this stuff it sound like the smart/safe way to start is to start small; avoid bottom brackets and fork crowns that require a lot of heat and focus on head and seat joints for a while.

I have some low-cost mountain bikes that I've pulled out of trash cans and parking lots. I think I'll start with those. The tubing will be a bit thicker which, as you point out, will be less prone to overheating. I'll make some mods and go from there.