I purchased a somewhat abused Clouser Illinois Terminal Box Motor on eBay a month or so back. The seller claimed he had purchased it in similar straits, and had attempted to convert it into something similar, but non-prototypic, before he lost interest. I was able to get it for a very reasonable price, and thought to restore it to it's proper IT glory. Unfortunately, I realized this wouldn't be overly practical. Possible, not really practical.
After much wondering/plotting/planning, I realized the ends would be perfect for any number of other cars, just needing replacement sides for a given prototype. This model apparently came in kit form, which I was unaware that Clouser had made available. The kit format with separate sides, ends, roof (unlike the typical Clouser full body shell), made removing the IT sides relatively easy.
I decided to build an Elgin & Belvidere box motor. The prototype, shown below from the classic Carl Gustafson work "The Dairy Route", shows the basic car body. It's a simple box motor design, really a motorized box car for LCL freight movements, and use as a locomotive for 2-3 car freights. A unique feature of these cars is the combination of overhead trolley poles, as well as 3rd rail shoes, as these cars operated on the Aurora Elgin & Chicago/Chicago Aurora & Elgin who not only interchanged traffic with the line, but also performed heavy maintenace work for them at their Wheaton shop facilities.
One of the original Clouser IT sides for comparison.
I was able to salvage these sides for future use, best of both worlds !
Head on view.