As to the import mark, I'll have to inform my buddy that he was in error as to the meaning. I accept the explanation given as that would explain why my 1950 Long Branch has the Century Arms stamp at the muzzle and no country of origin attributed.
I would ask the "old brit" who was in REME if he can explain the "R/REME" stamp on the butt? You must admit, for an otherwise unmolested Long Branch, it's odd to have a british butt plate and micrometer sight. That's what lead me to believe it had been taken into service by the brits.
As to he bore of this rifle allow me to say this. I've shot, restored, handled, repaired, collected,and/or loved many firearms over the 50 years that I've been involved in shooting sports. I can categorically state that this bore in appearance is equal to the bore of the '50 Long Branch which I bought unfired in the cosmolineicon, excepting the difference between two and 5 groove . I don't hold myself to be an expert and one thing I've learned is that there's ALWAYS room to be educated, but with a good stong light, I've looked at that bore from both ends and it is literally like a mirror. There is no sign of corrosion, pitting, fouling or any defect visible to the naked eye. If there is something amiss, it would only be detectable by the special tooling or gauging used in the production of these rifles. Short of you seeing it for yourself, I'd ask that you take my word for it.
BTW, I'm an ex military cop, and I bite back!