I figure you'll resolve the "play" issue (please let us know). As for the final alignment, to repeat my previous musings, I find it hard to believe you can find an off-the-shelf or plug-and-play optical (or whatever) module that performs the required function.
That said, if wiring, soldering, assembly, etc. is not in your comfort zone I was thinking about those super-miniature train cameras - they fit in N-scale for example. They are down to about $20 or so. They can send a "live" picture via Wi-Fi to whatever (whatever being an old unused smartphone, tablet, etc.). This would take some experimentation with focusing and whatnot, but perhaps you could mount the camera on the rotating TT aimed at the incoming tracks. The camera most likely requires DC power which would be derived from AC track voltage already on the TT using a $2-3 AC-to-DC voltage converter module.
