Cleaning up an OLD macports system

[Michael_google gmail_Gersten]

I have a mac that was heavily used three years ago, and has been
mostly idle for two years.

I've got a new install of Macports on it now, and a bunch of things installed.

However, when a  port wanted to install db46, it claimed that I had to
first remove the install from /usr/local/bin.

Checking shows a large amount of stuff from an old macports system
back from before the move to /opt/local.

Is there any good/easy way to tell what in /usr/local is from an old
macports, and clean it up/remove it, or is nuking the whole directory
the only option?

P.s.: This was old enough that it used SystemStarter items.