I don't believe it is a "pinless" frame, it is likely a "fixed" pin which is nonremovable using common tools( usually an interferance fit,pressed in). To be replaced,such pins have to be drilled out.Some O/U don't have pins,instead have hinge lugs. The Franz Jaeger Patent doubles have two lugs milled with a hollow cutter and covered with a plate. Maybe Raimey or Axel can come up with patent drawings.
Mike