Oh, hell, there are dakka threads proposing that Bastions gun doesn't actually have to go on the roof, you can just have it off to the side or something.
For that matter, our very own Jared think it's legal to put all 4 Heavy bolters of a Bastion on the same side?
One demon FAQ question I can think of is can the exalted flamer chariot think shoot it's torrent flamer thing when the chariot moves? (RAW it's pretty clear you can't, as it's a heavy, and it's on the flamer, not the chariot. But c'mon, the RAI is pretty clear in the opposite)