Well that's good to know. So if I find one in my price range at least it'll fit on my 30 inch turntable, with some overhang at each end.The overall wheelbase of the AC9 engine and tender is 113' so it should fit on a 120' turntable with overhang.
The turntable at the Dunsmuir engine facility was only 110'. When the big articulateds came along they built a two stall engine house next to the roundhouse and used the turntable as part of the siding. Engines would cross the turntable onto a track that led to the engine house without having to be turned.
This page has a picture showing the relationship of the turntable to the roundhouse and articulated shed.