I had the same thought. It'd be worth it to find a picture of the Presidents set and compare the photo to it.
The only obvious difference I see is that the presidents had their last names in raised capital letters on the base, if I remember correctly.
A Marx catalog is something I don't have, unfortunately. Though, O'Brien does have a Marx article in at least one of the editions of "Collecting Toy Soldiers".
Prost!
Brad