The Trainz SKU for this item is P11441391

and the B&O GP9's "torpedo tube" roof-mounted air tanks (located there to make room for larger fuel and water tanks underneath the engine)

Trainz Product Id: 12367679

Trainz Product Id: 11570956

That is determined by a railroad's loading gauge

Micro-Trains 09200362 N Southern Pacific 2 Bay ACF Covered Hopper #490394 ProductID_11398397 The Trainz SKU for thisThis is a MicroTrains 9200362 N Southern Pacific 2 Bay Covered Hopper #490394. These 2 bay covered hoppers are grey with black lettering and run on Barber Roller Bearing trucks. Built in 1975 in Huntington, West Virginia for the Southern Pacific Railroad, they hold a capacity of 2970 cubic feet and were used to transport dense granular commodities such as sand. Condition: Factory New (C 9) Operational Status: Functional Original Box: Yes (P 9)