MJ I do not know about other Air frames but as far as Cirrus are concerned the transatlantic ferry's need no modification and have enough range for the Iceland & Greenland Route, it is just the Australian ones as far as I know that need extra tanks and while substantially over gross weight I have never heard of any opinion it would effect the Air frame I also believe Cirrus support this opinion.
This particular ferry appears to be scuppered by a basic valve failure, I have no idea if they need to use specific approved valves or can literally pick any industrial valve of the shelf, pictures I have seen of Ferry tank configuration in the past do look like fairly random bits of kit plumbed in.