Thanks for that, and also for the hints in the
New Fast Galleons thread. Here's the result so far:

Flags and pennants are indeed correct. The "Ships_init.c" entry needed a bit of revision; it has the ship appearing in "Early Explorers", not appearing in "Colonial Powers", and it's French only. I reckon it's an advanced battleship, not an early one, and anyway one reason I want to bring it back is to use it as the flagship of Silehard's counter-attack on Bridgetown, which is where it showed up in Build 13. So, whereas the normal battleships are set to appear in "Golden Age" (0.3) and "Colonial Powers" (0.2), this one will also appear in those ages but with the values reversed.
Take a look at the second picture. See those ropes starting near the top of the mainmast and going down to the same platforms as the bases of the shrouds? I put those there - the first ropes I've ever added. Having read the bits about ropes in "New Fast Galleons", I went through the various model files for the battleship, checking that every "ropeb" had a corresponding "ropee" somewhere, and vice versa, likewise for the "falb" and "fale" locators which were still present. The "rope" locators went into the 40's so any "fal" locator had 50 added to its number, then it became a "rope". But two "fale" locators in the hull model had no corresponding "falb" anywhere. Taking a guess from the co-ordinates that they were somewhere near the back, I turned one of them into a "ropee", put a "ropeb" onto the mizzen, then started the game and looked for a rope that hadn't been there before. I couldn't remember all the ropes which
were there before, but that didn't matter - because I'd only converted one, what I was looking for was a rope on one side of the ship, attached to the mizzen, which didn't have a corresponding rope on the other side. There was one, leading to that platform. I also noticed that the mainmast lacked the support ropes which the other masts have. So I moved the "ropeb" locator to near the top of the mainmast, converted the other "fale" to match it, and the result is what you see there.
Next: retexture it to a scheme similar to other large capital ships of the "Golden Age" or "Colonial Powers" periods...