Is this N scale? If so who made it? http://www.ebay.com/itm/Chesapeake-...352?pt=LH_DefaultDomain_0&hash=item43df8a20c0
If it is N scale I would think it would be very early. The metal floor casting and the ribbed wheels seem to point in that direction. Why not email the poster and ask them to give you the actual measurements. If over 3" long it is not N scale.
Here it is again... a Mantua HO 'operating' hopper (the bay doors open and close): http://www.ebay.com/itm/HO-Mantua-T...983?pt=LH_DefaultDomain_0&hash=item51d4bbe667