I don't know for sure about how it transfers over to higher end bikes, but I know Sears sold bikes in the 70's that had internal cable routing for the rear brake only... They were Austrian made, and reportedly by AD or Puch... they are heavy and not up to their usual standards of their "cousins" (except for the rare 531 models) So, looking at some of the Austrian vintage frames may get you lugged steel and internal routed cables.