Although I might advise you that Bob is more of an Opel-engine fan, and not so much of a V-6 swapper.
Hmmm, truth he does speak (in my best Yoda voice).
I do personally prefer to keep it all 'Opel', but on the other hand I have always said that if
I was going to do a swap it would be a 60 degree GM V6. That being said, I have not ever attempted to do this, and consequently I will be of little help to you.
But, there are quite a few GT's running around with this engine in them, including many of the members of these forums. And there is a huge thread concerning one person's trials and tribulations regarding a swap to an EFI 60 degree V6 (Willit? Update
), so I suggest you start there and then dive into the engine swap forums in general, since this is one swap that has been done by many. Good luck.