Mark, I am really puzzled by your last hint. The April 25, 1954 IC timetable shows no line which runs to a state line and then stops, unless you count the line from Jonestown to Trotters Point, Miss. (crossing the main line of the Y&MV at Lula), and the IC had a ferry service across to Helena, Ark. And, this line was freight only before February, 1950. The only other lines that I see as being east-west are the Indianapolis-Effingham line (freight only before 1950), the Chicago-Fort Dodge line (passenger trains to the end), and the Meridian-Shreveport line (passenger service until in the late sixties).
The IC entered St. Louis over terminal roads, but I do not know of anything distinctive of a passenger train serving East St. Louis or the junction with the routes over the Merchants Bridge or the MacArthur Bridge. The train that connected from the Creole in Carbondale and the train that connected to the City of New Orleans and the City of Miami (through coaches to both main line trains) went through East St. Louis, using the Eads Bridge. The other trains to/from Carbondale used, I believe, the MacArthur Bridge. The Chickasaw and the train to the Panama and the Seminole ran through DuQuoin and not Murphysboro (the northbound Chickasaw carried the cars to St. Louis from the Panama and the Seminole.
There is also the line from Peoria to Evansville (freight only before 1950), but it does not seem to cross the Wabash in a due east-west direction.
I do not see any place other than the St. Louis area which could have had a connection with the MKT.