Proof Rosemary Willis had started looking towards the TSBD by Z-145

[Royell Storing]

I think you meant that she stopped filming before the first shot.  To figure out where JFK is on Elm St. all you need to do is see where the sightline from the camera through JFK extends to and then plot that sightline on a map of Dealey Plaza:

   The above would be perfect if Towner was looking through a monocular. And then she was panning too.