I've said here that I seek out models of interurban lines that had diesels and standard freight operations. Here's a fairly recent Atlas RS-1 that I recently converted to DCC with a Digitrax DH165A0 decoder. This had LED headlights, so it was an easy-to-intermediate level install. I don't know if Atlas has ever updated the Classic RS-1 to have 8-pin sockets; this one didn't.
It's shown with an Accurail Fowler boxcar also lettered for IT.
This site has prototype data on the IT Fowler cars.
[I]n late 1928 the Illinois Terminal ordered 100
unique cars that were taller than a Fowler, but shorter (less long) than a standard ARA boxcar design of the time.
The road needed “modern” boxcars to replace their ageing fleet of all-wood double sheathed boxcars, and their
mechanical engineers came up with an odd compromise boxcar design that was both familiar (short, and
comparable to the rest of their boxcars) and modern (single sheathed). The cars were remarkably long-lived, with
a few stragglers running into the early 1970s. That makes this little group of cars the last American-owned short
single sheathed cars in operation.
The Illinois Terminal's history with diesel operations is complicated. According to George Hilton and John Due's
The Interurban Electric Railroads in America, Illinois Terminal was a short steam line in the East St Louis, IL area that was acquired by the company that controlled the Illinois Traction System in the mid 1920s. The company adopted the illinois Terminal name for the entire system in 1928.
Two other steam lines between East St Louis and Alton were acquired at the same time. All were operated by steam under the IT name amd were never electrified.
IT RS-1 755 was built in 1950. The Atlas model is in the as-delivered paint scheme. RS-1s and some Alco
S-2s were used by the IT in the legacy steam service; I've seen DVD videos of them operating on non-electrified IT track in the East St Louis area in the 1950s.
Several IT electric interurban lines were upgraded in the 1930s with belt lines around cities to avoid street running and allow longer freights to be operated. These were originally operated with electric freight locomotives, Between 1952 and 1956, the IT abandoned all passenger service and removed the overhead wire. However, diesels like the 755 were used for freight service on the upgraded electric lines before the wire was removed.
After that time, of course, the Illinois Terminal was freight only and all diesel.