Welcome to C&V and thanks for posting. It looks as if your Aunt barely touched the bike. You are most fortunate to have received it in such a condition.

If it were me, I'd not worry about the correct crank as much as achieving the type of gearing you might need for the riding conditions in your area. So if you need extra hill climbing gears, now would be the time to add a triple. If not, go for a nice Campy, Sugino, or Dura Ace crankset from the late '70s era. Has your Aunt told you how she ended up with that crank on that bike? It looks very simular to the original one that came on my '79 Schwinn Traveler.

Best of luck with your Superior.