Markus,
What an impressive project in your link !
Porsche Boxster 986 - engine swap project - Page 1 - Readers' Cars - PistonHeads
In one of the Audi V8 swap Threads here I had suggested the Audi V6 as a more practical alternative but was ignored. Moot point because in USA the ever tightening Smog rules make engine swaps in modern cars in most States impractical.
Imagine how much more reliable/cheaper/profitable the Boxster would have been with this engine from the start. Not to mention the power upgrade with a TT option. And since it had an Audi engine it would have been differentiated from the 996/997.