I fitted a rover V8 to an MGB roadster which is more common then your engine change and had to go to the RDW which was not much of a problem in the end but it was 20 years ago.
Yeah, RDW was visited with the Giulia. Total cost under 100euros. Not a very big deal. Passat will be roadlegal as well so will need RDW approval. With a builddate before 1998 it's quite easy to get approved.