That’s exactly the story I’m

That's exactly the story I'm talking about 🙂

Camera is getting scratch audio, but multi-track capture is happening on an independent audio rig, to be sync'ed to picture later.

If I can figure out a way to rig up a poor-man's Genlock to Work Clock signal using an SDI from the A camera, there should not be any drift.

The real question is: is this possible?  Are there any boxes that can take SDI and generate black burst from it? 

and then I need to find a small box that can take black burst in and generate word clock out.

I have some big old rackmount boxes that would do the latter, but I want something a little more compact (if it exists).