Would be very interesting to see the proof marks. Wondering, if it were from 1980, whether it was proofed for black powder or some kind of smokeless load.
Looks to be possibly a bit loose with the rear of the rib showing proud of the breech face and the top lever notably over to the left?

I'd give it a go, what with a 24lb gun and typical heavy clothing that one would wear on the waterfowl marshes. Still.....not for the recoil shy or faint of heart.
A recreation of a WWII anti aircraft artillery exercise!

- Mike