The markings on the bbl look like they were taken out with a liner tool as used by an engraver for shading cuts.
The underlying X pattern is from going back and forth over the marks with a flat graver (maybe even the same liner) beforehand in a wriggle cut.
It pretty much destroys the ability to read what was there but sometimes under extreme power (20-30X) you can make out some remaining letters.
One of the hand held machinist inspection tube magnifiers (I think that's what they're called?) is handy for that. Mine's an old B&L and IIRC is 30x.
A line scale inside shows .010" in .001" increments, and everything is upside down,,,but it's handy anyway.
If the rib marking is hand cut, perhaps the same engraver was instructed to obliterate the bbl marking.
Most any bench 'smith of that time could handle a simple liner tool & hammer and could have done the job on the markings.
Just some thoughts..
