Ted, I suspect that a chamber as non-standard as 0.072" rim thickness, larger rim diameter, and larger throat to accomodate the .405 brass all say custom reamer. I don't think you'd get any manufacturer make those changes.
Shiloh chambers are reasonably tight, but I never had any problems with clearance with a 0.410" bullet, either in the Buffalo Arms or Bertram cases I used.
At the time, the Bertram cases were .405, thinned to 0.068" and then the primer pockets were deepened. I borrowed a lathe with a home-made collet for some of them, did some others in a cobbled setup on a drill press that produced chatter. They shot well but didn't look very pretty.
Clarence