If you are building you turn table from scratch, you could drill a small hole in the pit next to the turn table when the tracks are lined up, and put a small eyebolt in the side of the bridge to serve as an indexing device. Use a small finishing nail with the point dulled with a file as a lock by dropping it through the eyebolt and into the hole in the pit. If the eyebolt has a wood thread on the end, small adjustments could be made in the table indexing by screwing the eyebolt in or out as needed.