I'm with Gunman, these marks are a bit fishy.
No marks on action, very fishy.
The proof marks on the barrels are pre-1904 black powder, 20b chamber, nominal 21 proof size (0.605-0.615").
I would guess that the barrels were from another gun proofed as above and transplanted to this action.
Technically the chambers could be anything under 3" as there was no specific chamber length mark until 1925 other than an LC in the diamond for chambers over 2 3/4" proofed for heavier than normal loads. Sorry, really unhelpful!
However, the normal chamber length in the UK at that time for 20/16/12b was 2 1/2" so one could assume that if they measure 2 3/4" they have been 'dropped'.
I would consider the proof marks as an irrelevance purely on the basis of no marks on the action. The rest is arguable.
