Let me inject another consideration into the discussion. If you simply connect the GV unit to the back of an existing transmission, you'll end up with a monstrosity that's about two yards long. You'll be lucky if you don't have to do significant surgery to the trans tunnel in order to gain enough room to be able to fit it all into the car.
With that in mind, when I put a GV behind a C6 some years ago, I got the shortest combination possible. GV offered me a replacement output shaft designed to be just long enough to stick out of the main case. An adapter and a coupling and the GV BECAME the extension housing. It was only a bit longer than the original had been.
I had to tear the C6 down completely, since the output shaft is one of the first things to go into an otherwise empty case. But I did a bunch of work on the C6 anyway, so it was actually very little extra work.
Might this same approach work for you?
KS