Found this photo of a long MONON departing Dearborn as the Photo of the Day on Classic Trains website. Though similar to many others, I don't believe I've ever seen this one before. Note no "Lee" ad on the background building, but black roofs on the F3's with letter suffixes on their numberboards. I would say it's around 1950 or 1951.
The Classic Trains caption says it's the "Thoroughbred" but I wonder, given its unusual length and "foreign" cars mid-train. Any ideas? Maybe the day before the Derby? /Tim