Need ID of an indexing thingy

Someone gave me this, disassembled in a box, way back in the mists of time. I finally tried putting it together and got this. I think it had a heavily mangled indexing plate when I got it, but if so then it's long gone.

The indexing plate would have mounted on the end with the handle. The handle has a pin that sticks out (or should be) to engage with the plate, nothing unusual there. There's a bevel gear set inside the body. The flange on the body with the holes stays still, there's no shaft sticking out of the back side. The part towards the viewer with what appears to be indexing marks rotates when the handle is turned. The half-round bit appears to be half a roller bearing race that looks like it might be intended to mount on the end of the pin that's moved with the handle. The long shaft isn't screwed all the way in, it can rotate so that, if the bearing race was mounted on the end of the pin, the race would engage with the part with the index marks - the ID of the race matches the OD of the part with the index marks.

Oh yeah, for scale, the round bit with the index marks is 3-4 inches in diameter.

This might be shop made. If so then it's a pretty good design and construction job.

Anyone have any guesses what it goes to?

I’ve seen similar contraptions to mount on the back of lathe headstocks to index the spindle but without more pics I couldn’t see how this one would attach