Probably one of the most photographed railroad sites in the U.S. or at least in the top ten!
Here’s a view from 1976 when things were looking pretty shabby:
AMTK-422-E9A-CHICAGO-IL-JUL76-PRESTON-COOK by John W. Barriger III National Railroad Library, on Flickr
The Amtrak train is occupying the same (nearly) trackage as the pair of K4s above.
I’ll have to look for a decent track diagram. I do have this small diagram that shows part of the area here:
PRR South Branch-Alton-Jct by Edmund, on Flickr
This discussion has more information and may answer your question:
Cheers, Ed