The stampings on that barrel are of the style during the pre'-64 days. Especially, the '55' stamp on the bottom suggests this barrel may not be the one originally fitted to the receiver..
At the same time though, the bolt is a PF style. If the breech is of the PF style then I'm thinking a gunsmith at some point did the mods necessary to fit a pre-64 barrel to a post '64 action and removed the sight node at the same time..
Hard to say for sure.. An interesting rifle, that..
