Ted,
That model is an Athearn RDC-3 that was produced around the mid-1950s. The key ingredient to the power delivery were small rubberbands, one for each axle, that wrapped around the motor driveshaft. Actually, other than a wobbly start, the mechanism was smooth and quiet.
Like its passenger cars, the RDC was shorter than scale in order to follow the tight radius of most train sets.
Here is an ad from 1954:
Santa Fe never ran the mail/passenger combo, but they did run the RDC-1 full passenger cars. Two color schemes were used and MicroScale decals issues a set of decals for both schemes.
If interested, Life-like Trains has recently produced the RDC family under the Proto 1000 Series with full scale length and a very smooth drive-train.
-Ed
