I'm thinking about going with the Audi 2.7T for my mid-engine 911. This is what sparked my interest in that motor.
https://www.youtube.com/watch?v=lEtNMxVKegM
They did a single turbo conversion on the one in the video, but they come with twin turbos from the factory. It's a pretty stout motor in stock form and not too hard to get 600hp out of them with some bolt-on parts. The more I read up on the 2.7T, the more I like it. Heck I'm half tempted to put one in a boxster. The biggest reason I'm leaning toward the 2.7T, is their size. It's only roughly 18 inches long and they're dirt cheap. You can pick one up for just a few hundred $$. I had the chance today to see one in person and get some measurements. I took a 6 speed along with me so I could see how well they mate up.
The dowel pins are just a hair too big and keep the engine and trans from mounting flush together. That would be an easy fix by just drilling out the dowel holes.
This is another problem when trying to mate the Porsche 6 speed to the 2.7T. The starter is in the bottom right corner. Still not a hard fix. Just cut out an area for the starter nose and weld on a cover.