The Internet has really been helping me lately. http://terraserver-usa.com/ has digital aerial photos and topo maps you can print off. The aerial photo for Gibson City is from 1998, and the topo map is from 1984. A bit after Wabash, but they still may be useful.
Also check out websites for local libraries, and university libraries. For instance, Virginia Tech has the archives for the old Norfolk and Western, and a ton of online digital pictures covering almost the entire system. This includes lots of aerial photos of yards and facilities. I am sure Illinois has a State Historical Society. Maybe they have online resources.
There is also a Wabash RR Historical Society. You might try them.
I bet you are like me, a long way from the line you want to research. My line of interest is in Northwest Indiana and Southern Michigan. I live in Kansas. I have made two trips along the line and discovered lots of structures I did not know existed. My next trip will be to check out info at the small local libraries and museums.
Hope this helps.