The frame would have been one of the type that was cast in the mold originally intended for casting stainless frames, and would have been cast by Hitchner.(the original one-piece mold, used for serial numbers from 3660 up through D9999, was set aside). And, not meaning to be too picky here, but I believe it would have still been Foster Industries (i.e. not Caspian yet) that machined the frame. ...Deeton