One of the first locomotives I purchased was this one, which is a hybrid model. I know that other modelers in the period had the same idea, as I have seen other models that were converted in the same manner. The model is either a Star-Continental or Nason Railways 4-4-2 that has been converted into a 4-6-0 by replacing the original drive with a drive from a Scale-Craft 4-6-0. This particular one is lettered for the Yorkville and Western, the personal line of Fred Schorr, of OO brass import fame. The boiler is sand cast bronze with a brass cab and tender. The S-C motor was replaced with a large Pittman motor, and a smoke unit was added as well.
I don't know if there is a way to tell if the original model is Star-Continental or Nason. So far as I know they are exactly the same model. Star-Continental produced the model from 1937-39 and Nason produced the model until WWII. Other Nason locomotives are marked on the frame with their "circle N" logo. [See also this UPDATE].
I also have a frame that would have been correct for this locomotive that was in some parts I purchased. It is not marked with the circle N so it could be Star but I don't know if Nason changed that in later production or not. This frame has also been modified a bit, I would guess because the previous owner also had trouble with the original drive.
In any event it is a sharp model. The original was marketed as a PRR E-6 Atlantic but actually it was a freelance version of a K-4/K-5 Pacific, but built as an Atlantic. And it is heavy! Have to love that sand cast bronze.
UPDATE: The down side of this model is that not long after this article it quit running. Taking the gearbox apart the gears are clearly shot. Perhaps related to the very heavy body on a drive not designed to drive all that weight around. I will in time rebuild it though, I have the parts to do it.
UPDATE 12/2014: Finally! I was able to change out the gear. As with many projects put off, it was easier than I thought it would be to do. The engine is together again and running well ("backwards" compared to NMRA standards though, Fred Schorr wired it up that way, not going to change this element).