Do you have a shifter yet? I have a TR6060 from a '10 Challenger to put in my Barracuda. A Tremec rep told me it wouldn't fit because of the shifter location being so far back. Its obvious that the shifter from the challenger is back too far, but can get another shifter that would mount on the "rear" location.
I'm going through the same install right now. I'm looking at a Core shifter that mounts at the rear location and is even with the original four speed shifter. It's just a little to the right.
I've had to cut quite a bit of the floorboard and a little firewall out but it'll be worth it.