2 1/2" chambers but not marked 65MM. A bit strange. I think its certainly older then the 1980s.
Tut;
The Bimingham proof house viewers mark that you can see at the rear of the left barrel flat (a circle with a B and a 1) was used starting in 1979 through the 1980's. I agree the whole thing about the proofing and the absence of other proof marks from Europe on the flats is strange. Viewing the photo, the barrels and the bottom rib I can see markings and if the original poster of this could supply a good clear photo of these markings maybe that will help with the mystery of the guns age. The markings on the bottom rib are likely the name of the importer, required by the ATF. As to the 65 mm vs. 2 1/2" chamber markings: apparently, the proof houses were not required to use metric markings until about 1989--you can also see that the bore size is in inches. If the original poster will provide a clear photo of the viewers mark, I can determine the exact year the gun was proofed.