The 6speed AT in the Camaro and G8 mount right behind the motor though, right?

 

Yup.

 

about how much would a low miles vq 5.6 cost?

sorry to bump this but its a good thread plus i wanna do a swap in my 2nd gen sedan

 

It will cost a lot and you don't get much power for the cost. 420hp with a small expensive aftermarket. LS swap as already mentioned will get you much more. I just drove a CTS-V a few weeks ago and it's a blast. It's not hard to get mid 400s out of an LS without forced induction. Add a turbo and you are good for tons. I know some 1000hp street cars using LS engines.
Pick up an iron block 6.0 from a truck, swap on some LS heads, LS6 intake, and with exhaust you are above the 400hp mark already. And you will get mid 20s for mileage. I got 18mpg in a 2011 Camaro SS over 900 miles this past weekend. And I hammered on it plenty of times. Those LS engines are a blast.