As I said before, i emailed the author of Picasso96 about the driver development kit. What follows is his answer:
Sorry, development of Picasso96 has stopped years ago, its code base has been integrated into the sources for the next Amiga OS releases, and to be honest I do not even have the necessary files accessible any more because of inaccessible hardware. And besides I could not give you any support you would surely need because I probably have forgotten all about it.
I am really sorry, but you are about ten years too late... ;-(
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Mit freundlichen Grüßen,
Tobias Abt
But still, i am not gonna give in so easily. There have been many users which have created drivers and hence used this driver development kit. I will ask them for it. I might get lucky.