Look between the boiler and the chassis and see if there is a direct worm gear slanting down on top of the bull gear. If so, it can be anywhere in the past 30 years or so. If there is a gearbox and an open frame motor, then it is quite a bit older. If it has a gear box and a can motor, it is one of the last production ones. Looks like it has been detailed a little bit, but appears to be missing the pilot. These can be turned into some fine-running models. Looks like the third set of drivers have flanges instead of the original "blind" ones. I would probably leave it alone unless you are planning on running on 15" radius curves (although you might find a problem on 18" radius).