Hi Axel, how is the project going?
I was just watching a series of youtube videos by Davide Cironi on a Countach replica being fitted with an Alfa V6/Audi transaxle combination. There are some interesting shots of the process even if lots of details are skipped over. My grasp of Italian isn't enough to understand much of what they are saying. They appear to have made the adaptor plate from layers of thin steel. The V6 is from a manual Alfa 166 2.0 V6 turbo.
https://www.youtube.com/watch?v=jZurA6Vwj1s
cheers
Ross in NZ