Dude~,
Since you've already flown the Duchess, if you're near London, you might want to have a look at
Wycombe Air Centre who have a pair of Duchesses, and offer a multi rating package (look in the training courses section of the web site).
I've been a satisified customer of theirs for 11 years now. I did my multi rating with them in 1999, and IIRC it only took a couple of days.
Brooklands