If everything is different -- including the title -- I wouldn't mention that you've already queried them, especially after six months, IF they didn't ask for more pages. On a flat rejection or a no-respond, I'd just pretend it was a new project.
Many of them can search their emails by your name and project title, though, so be sure it's very different in case they feel like they've seen it before. Most of them dislike requeries.
If they did ask for pages, then I would remind them that they had, and tell them that you've revised significantly.