You might be able to do an OEM LS7 with the A6 and use all the oem harnesses but modify them. These guys have done it to a C6 Z06 but I don't know any specifics other than what is posted. He would be a good place to start talking to.
http://forums.corvetteforum.com/show...=Z06+automatic
You can even mod the LS7 with a nice cam and add a higher stall converter.