I don't know what specific fabrication techniques were used, but I suspect they may have been fully hand crafted in a job shop. What is cost prohibitive and impractical today was commonplace fifty years ago.Even a table radio from those days is incredibly labor-intensive by todays standards. Point-to-point wiring was replaced by printed circuit boards and pressed steel and injection molds replaced hand-made cabinetry. The cost of labor just makes hand assembly prohibitively expensive.
In that spirit, the work of Michael Christ is incredible, isn't it?