qI'm responding, but I don't know the answer to your question. I am not
familiar with Mailman, or how to move archives on to sourceforge, or if it is even possible.
i have been in contact with Paul Dubois and i am tracking down the feasibility of making the transfer happen. it amounts to cat'ing the mailbox from the matrix sig archive onto the sourceforge archive, and re-running the archiver on the resulting mailbox (according to barry warsaw).
so we need to find out if sourceforge allows us to fiddle with the mailbox in that fashion.