Hi John,
Agree - sounds very messy!
With regard to any 'ranking drop' I really wouldn't worry about this either. I had the same concerns a few weeks ago when I redirected my entire website (an old keyword loaded domain to acornseo.com).
I did a quick audit of the site using Screaming Frog to get all the links, then 301'd each one individually to the new location. The process was very easy, the time it takes depends on the number of pages your website has.
Looking at the Google results after I made the change, I could see my new links appearing in the results, just below the old ones. After a few days the old ones had disappeared and the new acornseo.com links replaced them completely - in effect I had zero ranking downtime, and haven't seen any loss of position since the change over.
Hope that helps.
Cheers,
Andrew