Restoration, apart from being hard work, has to be true to the original state of things. When that means restoring the engine-room to what it was, that means finding an engine and generator the same as what was originally installed during the war. For Stony Batter, that meant finding one in Hull, Yorkshire, England, dismantling and shipping it out to New Zealand, then painstakingly winching it along to the engine-room. But the tunnel originally used had been concreted off, so that had to be removed first.
Where the pump-shed used to be during the war. It had long since vanished, leaving only the foundation.
Restoration by society volunteers in the twenty-first century, well under way.