It's offset 1 1/4 inches towards the passenger side. For a truck it isn't an issue, and on a car, you still might have the necessary clearance down the tunnel. Good luck.
Oh, and your second question- driveline to differential. The 8.8 that we installed is mated to a Tremec TKO500. My brother had a guy come up and measure the distance, and he's got all of the parts as well. It's going to cost my brother about $300. So, the answer is that I don't know yet, because I haven't done it on my own truck. But I will know in about 2 weeks.

Also, Bill's got a good point. The two 8.8's that we bought, we pullled from our local "pick-a-part" for $75 a piece. Including the rotors, calipers, and pads. If you look on the tag make sure you see the L in front of the gear ratio! L37 8.8 blah blah blah!
Heber City, UT (15 mins outside of Park City- basically it's in the mountains)
55 Effie