As Gert asked me by PM: The action is a typical M-S 1956 “Magnum” action, straight, low bolt handle, bolt stop spring placed higher on the receiver bridge to make way for a reinforcing boss that serves the bolt guide rib as a third, safety only, locking lug. The bolt is polished bright as on all M-Ss intended for the American market. To date it closer, look for the Vienna proofhouse NPv Nitro proofmark, maybe covered by the wood. Besides this mark there ought to be the last two digits of the year.
The stock left the factory as a MC stock with an exaggerated “Monte Carlo” comb, designed for Stoeger and intended for scope use only. It shows other influences of the then fashionable Weatherby/California style too, like the white-line spacers. As the rifle was never scoped, the MC stock was highly impractical for open sight use. A former owner had the comb line lowered and the exaggerated cheekpiece hollowed out to make it usable with the open sights. Such trimming down of MC stocks was quite common and led to the creation of the more restrained MCA stock. So the stock is not “factory original” anymore. There is no reason why you should not modify it further to suit your shooting habits.
Mannlicher-Schoenauers in .458 are very rare. At the time they were offered the pre-64 Winchester 70 was the “in” big game rifle, praised by American writers and cheaper to boot. The British usually preferred Mauser M98 actioned rifles. Because of the forward position of the bolthandle the M-S rifles were badmouthed then by American writers like Elmer Keith as “slow to operate, unsuitable for rapid follow up shots”. During the 1950s very few European hunters could afford an African safari. So there was little demand for a Mannlicher-Schoenauer in a “stopping rifle” caliber. As I wrote before, even the “magnum” Mannlicher-Schoenauer action is too short for a more flexible magnum like the .375 H&H, further diminishing the popularity. And, factory fitting a .458 rifle with such a stock designed for scope use only can only be described as an outright bum idea. So here you have the reasons why Mannlicher-Schoenauers in .458 never sold in high numbers and are rarely seen today.