Crazy suggestion, just connect two normal keyboards. Particularly if the left one is numpad-less you’ll get much of the idea for sure.

They might be a smidgeon further apart than might be ideal, there’s some ugly duplication… which happens to enforce a minimum distance… just get that shoulder opened up and start evaluating. It’s certainly likely to be more optimal than the status quo.

Might need Karabiner on macOS to keep shortcuts working.