Hi Magnus,
I've been looking for quite a while for something on this subjet, but can find very little. In fact, there's precious little documentation on repeaters in general.
As you're in Switzerland, I wonder if you could contact the PP museum to ask to look in their library. They have a large collection of books on the top floor of the museum, and apart from anything else, it would be great to have the cases unlocked and to have the right to sniff around
nick