Mark, Matt - Thank You!
The turntable was an early modification to the layout, but after I had already built the frame structure, plywood, etc. Initially, that area was for the several times listed/announced Lionel Rotary Coal Tipple - last time in the 2011 Vol-II catalog; but which never materialized. So in September 2011, seven months after I had started the layout, I decided to cut a big hole to fit the magnificent 34" Millhouse River Studio Turntable. This turntable size would be suitable for my MTH Premier Big Boy, and unbeknownst to me at the time, my future Lionel VL Big Boy as well.
Matt, that small rectangular hatch was there first 
Cutting the 2x4 frame through the 5/8" plywood was not fun, but at least I had not yet installed all the QuietBrace over the plywood. I had to cut several cross braces and add others. (Pictures from Sep 2011.)
The turntable is held up in place with six 1/4-20 nylon thumb bolts (into the plywood) plus two steel 1/4-20 wing nuts on steel studs that protrude down through the plywood.
The most challenging part was how to hold the turntable up, in place, while I worked on it. A furniture dolly, a saw horse, and some spacers did the trick.
Thank!
Alex
