Hopefully you can bring back the old posts, but I think the inactive projects should all be moved to other projects or something. The issue is that if a small board has like 30 sub-forums, it looks emptier than if it has 10, because all posts are more spread accross the board, so instead of 100 posts per section you end up having 33. Later when a lot of discussion occurs in a specific area then you can add more sections I guess, same if people requests a new board.

I don't know if I'll be active much on the calc side but I'll try to show up during my weekly visit on other boards. Also, I like the forum theme. Is it a custom theme you found somewhere or one you made yourself? I even think maybe the main site should be themed like the board, or even integrated, assuming PHPBB3 has the required mods for that.

As for the post I guess it's fine since it's kinda more calc-news/major sites update related and less active members might wonder what happened to old posts or have the old link bookmarked.

Suggestion:
-Make sure the old board is now read-only, so its history won't get invaded by bots.
-Make sure all sections on the old board now shows every topic instead of cutting off the active date to 30 days.
-Add a notice at the top of the board saying the forums moved and the new URL.