John, you forgot Matska #177 with double barrel set I owned some time ago, I brought it from Finland.
It looked like twin to your boxlock, but weight was 3,2 Kg with 28" barrels. Second set of barrels was heavy 32" for goose and swans. Both bbls made from Witworth steel by John Kilby.
Both barrels had only the first provisional London proof.
Your gun been imported to UK before importing to US, that's why we can see full set of London proofs on flats.
The gun #17 has made in 1883.

Geno.