Given the condition and (what I know of) the history of this car, I'm confident the ignition/locks are original.

Found a reputable locksmith. They made a factory-spec copy from an "old key" database, all they needed were the model, year, and busted key for a comparison.

The new key works! I was concerned as it's missing some of the smaller contours of the prior key (which was also a copy, but likely a direct copy of the original). A little stiff in the door, but the car starts right up. Only cost me $20.

Thanks for the tips, all. Funny how little it takes to turn a car into a 3000 pound paperweight.