rgunnz,
Sorry, 4100 it is.
A 4100 would have come standard with dual rear wheels.
Here are 1952 4100 models - 1952 was quite similar to 1951 (some of the 51 illustrations are missing).
You say you saw it listed as a 4100/6100, please let us know where you saw that information, so we can speculate (post a link to that information).