The Mount Claire Roundhouse, located in Baltimore, MD which is now part of the B&O Museum, has the reputed prototype for the Atlas turntable.
Supposedly, there are several other examples of a completely covered deck turntable, but I have actually walked across the B&O turntable.
Back in the day, Atlas, was searching for a prototype turntable that they could use in their Snap Track line, and this one was readily accessible.
I have no clue as to whether the dimensions match, but a relatively small 4-4-0 like the B&O wood burner "William Mason" ( reputed to have hauled Lincoln's funeral train), fits on the prototype with room to spare. The only certainly, is that the Atlas turntable, matches a 9" section of Snap Track.
Back in the '90s Model Railroader Magazine contained an article converting the Atlas TT to one with a pit. Essentially adding deck bridges to the top and depressing the assembly to match the rest of the track. I have one, that I was going to convert, but never got around to doing the project. Meanwhile, Walthers came out with a more suitable 90' turntable.
Joe