At the risk of muddying the water slightly, I have a 312 with smoke/choo-choo in the boiler and the four-step reverse unit in the tender. I claim (without a whole lot of specific evidence) that I received it - along with the New Haven passenger car set (baggage car and two coaches) - the Xmas I turned 6, which would have been 1950. The 1950 catalog doesn't list the 312 any longer, but the 1948 and 1949 catalogs do (actually, the artwork shows 312, the text sez 312AC) along with the New Haven passenger cars, showing them as a set. So I dunno. I suppose I could have been 5 (Xmas 1949)... I am certain my parents bought the train set plus the 8B transformer at Gold's Department store in Lincoln, NE, so this may have been a set left over from the previous year or ...?
That engine still runs well, though I do need to replace the nichrome wire in the smoke unit
