As a sidebar, relating to sand-cast versus die-cast, in the two-stroke world of 4 cylinder Yamaha competition engines, most engines came from Yamaha with die-case crankcases, though in the late 70's there were sand-cast aftermarket versions available, made for/by Yamaha in the USA. These cases are better in practice (though of course have no engine/frame provenance), as they were easier to weld without warping the cases (required if a rod came through), were stronger and apparently had a little more crankcase volume (not that this is relevant in 4 stroke discussion).
Legend has it that the sand-case cases were actually copied from the works magnesium cases.
Were there mag-alloy Gold Star crankcases? I suspect so - there were mag timing covers, rocker boxes and gearbox cases.