Turntable build part 1

I've been slowly chipping away at my turntable build. I had two turntables on my previous layout. One was a wooden gallows turntable, which I'm keeping for the town that will feature at the other end of the new modular railroad. However, I wasn't happy with the turntable that used to be placed at Erewhon on the old layout, mainly because it was mainly a freelance design as I hadn't seen any photos from the turn of the 19th century with anything that looked close. 

Earlier this year we visited the Pleasant Point Railway, which is not far from Timaru and one of the attractions was helping turn a rail-motor car on the turntable, which had a pit, with the turntable bridge being the more conventional design with the girders underneath the track. I decided to model something similar and found some prototype pictures of turntables from the period to give me something to base it on loosely. 

Northern Pacific Railroad roundhouse at Lester, circa 1910

‘Colorado Midland Engine 20 on turntable’

My turntable bridge was made from a piece of 20mm plywood. I carefully measured, cut and centred a bit of straight set-track. I reused the girders from the previous turntable. I will glue them on later, presently they are just resting in place for the photo. I've had a go at carving masonry blocks into insulation foam for the turntable pit wall. I'm pleased with how it turned out. The next step will be to paint the stonework and then glue it into place. Then I can lay the pit rails to power the turntable. The last thing will be to add decking, made from strip wood and balsa to the turntable bridge. 

I am considering adding a hand crank to rotate the turntable. My main concern will be to ensure it is geared low enough to be easy to turn and accurate enough to align manually. I may just settle on turning the bridge by hand. But I would like to watch the table turn around, seemingly by itself.