Thanks @James_Carl, @Ben_Brenner. The asana.kothar.net tool does allow copies within the same workspace, and copies comments, however there is a limitation: comments can’t be created with the original authors intact, as the tool is acting on one user’s behalf. It creates a single comment with a log of the comment history instead.
If you are rolling a project over each month by copying a copy of a copy, etc. this may lead to some weird effects.
Mike.