I was shown an 'in the white' bbl'd action back in the 90's at a local shop that had come in for sale.
It was a Belgian marked Model 98 commercial.
(stamped 'Belgium' on the bottom of the front recv'r ring flat right behind the recoil lug)
In 270WCF and had the exact same engraving pattern on it as the OP rifle.
The shop owner,,a very knowledgeable gun person in the biz since the early 60's said it was factory (FN) engraved and I had little doubt also.

I never got a second look at it as it got bought (supposedly 'promised' to another customer of the shop.) ,,and so it goes.

But I remembered that engraving pattern as soon as I saw this thread.
I've been an engraver for just 50yrs now and some things just stay with you for some reason.

That's all I have to add to the discussion,,other than I too would never have left that 458 behind in that shop!