I'll give it a go.
Based on the picture and given the known size of a full size T-12 and the age of the photograph, the scale would have to be an fractional inch based scale. 1/4" would be way too small, 1" to the foot would given you a model around 57" long a little too big, 1/2" to the foot looks about right.
So that means in HO scale that would be a 1/24 scale model. So that would make the model in HO scale referencing full size a scale of 1:2088! You could certainly 3D print such a model, but major applause if you can squeeze a motor into that little gem!
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Art Dutra
Meriden, CT