<>The above photo shows the "HO" Plymouth with an S scale F unit.
How close is this to correct S scale?
I have not found dimensional data for an M series unit.
For photos of Prototype Plymouths, see
Some photos show freight cars in the background.
Based on these photos, the model certainly is close in size, even if
not exactly right.
Here are the S scale dimensions of this model:
Width: 7' 9"
Height: 9' 10"
I have not found a photo of an M unit that exactly matches this model,
although I have found units that are quite similar, for example, the
cab front window configuration is very similar to that of EBT #M-5-A.
Note that the prototype photos have a hood side extension on one side
only, vs both sides on the model.
Several prototype photos show air tanks behind the cab vs a "toolbox"
on the model.
Note the high coupler location on the prototypes.
I suspect that this model is extremely close to correct S scale.