Just had a look under the back of my car, and I can now see where the tank would conflict with Hydragas units. As my tank is already showing signs of rust at those bottom corners, it looks like a new tank would be a good idea in any case.
However, seeing as it needs to be cut and shut to clear the spheres, I might try to increase the capacity at the same time - it looks like it could be extended rearwards, certainly on the left, and possibly elsewhere as well. I'm not after a massive increase since that means it would mean increased weight on the tank mounts, but an extra gallon might be worthwhile having.
But am I just being greedy?