Ok,
I am fiddling. I have a question - Do you have a lot of engines that you want to be able to change? If yes, are they steam or diesel?
I tried fitting the Atlas O turntable. It's can be located and can be made reliable or to run depending on the condition when acquired. It's a little easier to install and a lot less expensive than others.
A turntable just seems too large for the layout space. Having scenic items would finish the layout nicely.