Marantz Imperial 9s
Peplepew,
Wow, your post sure brings back memories. I bought a set of new Imperial 9s back in the mid 70s, and for the money, and the competitively available product in their price range, they sounded great. Of course, you're absolutely right about many of your assessments - the woofers were weak and bounced all over the place, the tweeters seemed to roll off early, but the mids were sweet.
I don't envy the project you're about to undertake, having built one set of speakers myself with only semi-good results, but there are a lot of people that have the DIY fever on this site. Get these members to comment.
Good luck, and keep us informed on your progress.
Pat