Look here for pictures of mock-up and conceptual images: http://notreally.info/transport/planes/avenger_ii/a-12/img/
By my eye, neither one is totally "correct". That said, I doubt the mock-up would show the actual expected configuration of the exhaust(s), as these were usually a closely held secret on stealth a/c. My first viewings of F-117 and F-22 were with the a/c backed up to a wall, cordoned off, and armed guarded. There is at least one concept/engineering drawing out there that shows twin exhausts.
John