You should be able to at least date the age of the piece by the proof marks.

There should be date code letter mixed in with the proof marks somewhere. 1947 was 'z'. Then they started over using the Greek(?) letters.. Alpha, Beta, etc. When those ran out they went back to standard small case letters with a bar underneath.

Here's link with a couple of charts with the date codes on them. One of them has the the Greek letters printed out in cursive so you can kind of figure out what they are.
http://damascus-barrels.com/Belgian_All_Proofmarks.html

There's also a proof controllers stamp in there too. A capital letter with a '*' above it. That's separate from the date code. It is a stamp assigned to a specific individual at the proof house.

The action if sold as a component alone may not have had an FN stamp on it then. The action in many European countrys is/(was) not considered the 'firearm' as it is in the USA.
In some, the bbl is. In the case of the Hi-Power pistols from FN,,when they shorcut the mfg process a bit and abbreviated the serial numbers on the bbl and frame,,the full serial number on the slide of the pistol was kept as the slide was considered the major firearm component at the time.