Don't believe that FN action is a Sako. They used the 300 Series actions that yet used the striker mounted/impinging more traditional mauser safety. The rifle here reflects a typically later trigger impinging tang-side safety. The bottom metal looks a bit strange but perhaps cameral angle. If it is steel, that places it most likely at the end of fifties FN production. If alloy, into the sixties.
FN sold actions, barreled actions and complete rifles. From the early sixties it was more popular among rifle makers to import the FN barreled actions to 'have their way with it'!
I'd expect to see the bolt shroud striker mechanism of the latter 400 series "Supreme" action which did utilize the trigger safety orientation and such type trigger. Whether that trigger is original, I can't say. The above comment concerning the serialization of the Sako FN mausers is point on. The Sako of mine in the pix below is SN 105K. Sako did not make many of these. They intro'd their new L61 action in 1961. My lowest of that model SN is in the 11K range. Point being, differing SN range entirely!
It may be fun to speculate, but really toward little end unless concerned about indications of 'mix 'n match' components. The French Walnut stocks on the complete FN branded complete rifles of early-mid fifties became too expensive for rifles already priced the better part of a hundred dollars above the Win Model 70 of same era. The alloy cast bottom metal of the sixties breathed some new life into a cost saving species of the by then semi-classic iteration of the FN mauser. "Firearms Internatonal" marketed "Musketeer" branded rifles are typical of FN action or barreled action imported. Stocked and marked by the rifle maker firms here.
The nomenclature in your photo perhaps custom gunsmith, retailer or customer! Never heard of such and I don't know.
FN Sako Rifle & Action shots below.
Good luck with your project!
John
