There are lots of original pre 64 Win 70's in 338 and 264 with 1956, 57, & 58 dated receivers.
Winchester made a lot of receivers for the 458 in 1956 and 1957 before finding out that people weren't going to pay more than double for it from other calibers. The receivers were used to assemble it's offspring. All Win Mag actions have 458 stamped on the bottom of the recoil lug to identify the wider rails and mag well opening for the assemblers.
