I used to be heavily into Volkswagens years ago.
Now, keeping in mind that they are two entirely different animals, someone several years ago, sometime in the 1980's, had published a ridiculously detailed book on their conversion of a LH convertible to a RH, with all sorts of text and photos. There was also some heavy rust on it, of which all is completely addressed as well.
I would imagine it's still available someplace, reasonably priced, and while it's still just a rear engine VW convertible, it gives you a decent idea of the changeover process.
Of course, things have changed, I have moved on to the MB's, and I can't for the life of me remember the name of the book, but I would venture a guess that someone in a VW forum would know what one you are talking about.
Just an idea, really.