here is some speculation on my part, I think that the base may be from a Lyman 48 for a Winchester Model 52, maybe the slide as well. The part that attaches to the tang could be a casting with machining done afterward or it could involve no casting and just a fair bit of machining and hand fitting and filing.

I would say that whoever made it had access to at least a milling machine and most likely a lathe as well (for the knurled screw).