They are substantially the same as the Field Grades made after WWII by Marlin at the Fulton NY plant except that they have aluminum ventilated ribs, rather than solid steel ribs. I believe Marlin used epoxy (in 68-71) to strengthen the inletted wood surrounding the lockplates, which had been one of the problems with using modern higher pressure loads. Epoxy wasn't available when LC Smith Gun Co. made its last gun in 1950 but it is available now and can be used to strengthen inletted wood areas in older models to prevent chipping, cracking and even oil/solvent infiltration.