This set was sold in 1950. I suspect that Marx had some quantity of these engines printed up when we went into WWII and they could not sell them off for lack of parts. Postwar they decided to use up the inventory as they could. It's not especially pretty but there it is, a legitimate streamlined double A unit heading up a freight consist with one of the engines reversed!

These sets are somewhat hard to find - the dogbone coupler is often missing. Included in the set is the UP 3824 caboose on the brown frame. Now, you have to ask yourself why? Why, of all the cars that Marx made did this one get the brown frame? The 552 Groceries and Sundries gondola in the set didn't get the brown frame treatment, neither did the 553 Santa Fe tank car. Why the caboose? In millions of these six-inch cars, besides the blue passenger coaches in the Blue Mercury set, this one car got a special dedicated frame. Why?

Here are the engines and the special "dogbone" coupler.