In addition the font of the bbl ser# being different,,the 'Cal 280' was put there with either a pantograph, or a photo etch/ laser etch process.
It's not a stamped in marking and certainly not an engraved mark.
The methods of marking would lead me to believe the bbl was very recent replacement,,or at least the marking itself is.

Another thing I see is in the closeup of the rear sight.
The sight itself has the same soft edges/buffed and refinished look that the recv'r has.
I'd guess that the sight is the original from the rifle,,
The sight then refitted to the new bbl on the gun now, as the bbl itself has a sharp clean polish and blue.
Also note that the old sight does not fit the bbl at all well. The front edge not touching the bbl surface from about the 12 oclock position around to the far side in the closeup pic.

I'd do a slug of the bbl to determine to groove dia. See if the bbl is possibly just a common 7mm bbl (.284d groove). That'd explain the smaller than normal bore dia too for what you'r expect in a .280Ross. (.287/289d groove).

Though they are buffed over and somewhat tough to see,,look carefully at the Crowns on the recv'r proofs.
Then look at the (very crisp) Crowns on the bolt proofs.
They are different.
The Crown/U is especially easy to sort out.
The Crown/U on the recv'r has 3 'windows' accross it's face.
The (should be) matching Crown/U on the bolt does not.
Instead it has a centered window which forms a 5 pt star to the edges of the crown.

Those bolt numbers look pretty clean and crisp compared to the rest too.
But all this may not indicate a switched bolt,,but rather just a restamping of what was originally there and lost during refinishing.
It does indicate, at least with the proof marks on the bolt handle, that the marks themselves are not the ones stamped in at the time of proofing IMO.

These are things I see as an engraver and having worked in the gun restoration biz for 50yrs.
I've seen the best of work, the fakes, upgrades, the worst and best of attempts to deceive and the worst and best of restoration for what it is,,,to simply put back to some form of originality that which has been altered.