Big thanks to cordwainer for the information. One of the topo map links he sent was pure gold. I've clipped out the O'Hare portion of it, overlaid it with the CAB report map showing the flight path as a half-transparent image. The landmarks line up exactly, validating the CAB cartographer.
https://ibb.co/e4n1dG
Turns out the impact point was virtually on top of the A from my other image. I had guessed it was farther north.