In the postwar era Marx produced 6 different road names of lithographed metal diesels excluding the M10005 series: #21 Santa Fe "AA", #6000 Southern Pacific "AA", #62 Baltimore & Ohio "AA", #81 Monon "A", "AA" & "AB", #4000  Seaboard in "A", "AA" & "AB" and #54 Kansas City Southern "AA" and "AB". A "matching" tin caboose was offered and actually make a very attractive grouping. Plastic cabeece were offered in 4 and 8-wheel version for the Monon and Kansas City Southern engines. An example of the Kansas City Southern is listed in the very last photo.

Lets start with the #21 Santa Fe diesel (which was covered in the Plastic Diesel Guide ) that was produced from 1950 through 1952. The 1952 version came with plastic truck side frames and the earlier units were cast metal. As an aside, once again, I must include the Unique Rock Island "AA", though not a Marx product, as it is such an attractive offering:

Also introduced, at the same time as the #21, and ran  through 1953 was the #6000 Southern Pacific "AA" diesel offering which is modeled after the EMD F-3. There are 2 variations that exist. One with a silver stripe and one with a white strip. Shortly there after, the #62 Baltimore & Ohio "AA",  produced in 1953 through 1955. The #62 came with the same motor as the #6000 and in 1955 it came with a double reduction motor. The double reduction motor can be distinguished by the gear teeth being recessed from the edge of the wheel vs right on the edge of the wheel. The advantage of the double reduction motor is that it will operate at slower speeds and offer better pulling power. Some of the dummy "A" units came with a plastic fork coupler:

The Monon "AA"  was produced in 1955 through 1959 in various combinations of powered "A" units, dummy 4- wheel "A" units and dummy "B" units in both 4 and 8- wheel versions. The power units came with double reduction motors or rear axle only drive motors. A tough to find mechanical (wind up) Monon was also produced for a short period of time:

Also produced from 1955 through the late 1950's was the green, yellow and red #4000 Seabord Diesel. It came in mechanical as well as small motor electric versions. The mechanical is more readily available. Dummy 4-wheel "A" and "B" units were also offered:

Last in this series was the Kansas City Southern which was  produced 1956 through the late 1950's. Strictly available as an electric in both large and small motor versions. Offered in "AA" and "AB" combinations in a most colorful red, black and yellow paint scheme. The dummy "A" was a 4-wheel unit. The "B" units were offered in both 4 and 8-wheel versions:

The last 3 diesels (Monon, Seaboard & Kansas City Southern) are modeled after Fairbanks Morse engines.

The #21 Santa Fe was offered in a separate sale carton in both tab & slot and tilt coupler versions. From what I can tell the remainder were available in sets only, except for the #62 B&O and the #6000 Southern Pacific. Outside of the #21 Santa Fe the offerings were mostly freight sets.

Depending on your interest these lithographed sets frequently came with what appears to be different shades of lithography. A good example is the #62 B&O. These are unintended variations. This was how they came from the factory. The nicer the match the more attractive, so search for those best matches, if that is your thing.  This makes the hunt all the more fun.

These inexpensive diesels are colorful, reliable and meant to run!

Very best, Mike (lionelsuperotrack)

PS In order to make this article as correct as reasonably possible, Tasker Brush provided invaluable assistance with technical information. Also a thanks to Al Osterud for providing the reference to actual diesels.