Tech says the heat exchanger is hopelessly clogged. Pros on this forum seem to believe it's probably repairable if someone cared enough to bother cleaning it out.
Otherwise believed to be in generally worn but serviceable condition; relatively recent looking burner motor assembly and transformer, was supposedly serviced annually by the previous owner. Worked like a champ until this last cold snap.
Unit is installed in a mobile home in the Merrimack Valley region of Massachusetts.
If someone wants to come yank it out, they're welcome to it. Otherwise, the winning replacement contractor will get to haul it off to the scrap yard.
Given the age of this thing, I won't be surprised if a museum curator responds.