So, as a final coda to all this, I've just been zipping 'round Meiji Restoration-related sites on Kyushu, which included a quick visit to Shimonoseki. Unfortunately the battlefield my specific scenario was based on is now a suburb, but there's some (reproduction) guns overlooking the bay:
As well as a monument to the 1185 battle of Dan-no-oura:
And a cracking view from Mount Hinoyama:
Complete with the remnants of a later battery from 1885:
Incidentally, I forgot to mention it at the time, but my game managed to make front page in the local paper (supposedly!) (
https://www.oxfordmail.co.uk/news/23379581.wargamers-fight-overlord-game-show-abingdon/)