help me ID this drill press mortising chisel holder

[BTL-A4]

I have what I'm pretty sure is a drill press mortising kit chisel holder. I can't seem to find a brand or part number for it. A Google image search turned up empty. I looked thru quite a few parts diagrams as well. I typed in "Craftsman, Rockwell, Delta, Shopsmith and mortising chisel holder" next to the photo. All of what I saw was symmetrical, not like mine. Anyone recognize this?


Some context that might help: I found this when I bought a lathe. The owner had a stand full of misc stuff and he said it all came with the lathe. It was mostly Craftsman. There are no other mortising kit parts. I'm guessing Craftsman or Delta based on the color.
The hole at the bottom is Ø5/8", the opening at the top is 1.8" in diameter. It does not fit my 15" Craftsman Commercial DP.

Any ideas what brand this is?

 

[BTL-A4]

Has anyone seen this on a DP? I thought it could be Walker-Turner, since most of those seem to have a mortising attachment like this, but I would like confirmation.