If deeper is what you want, consider doing it yourself: cut the chassis at the bottom and rivet in some aluminum angle you obtain locally. You could also extend the bottom and sides with aluminum and rivets. "Pop" rivets aren't pretty, but they're strong and functional . . . and the modifications won't show, hidden in the dash.
If you don't want to do it yourself, have you considered having one modified right in Sydney by a fabrication shop? A little 6061-T6 aluminum, some TIG or MIG (TGAW or MGAW) welding and you have what you want. It would be done exactly as you prefer, instead of communicating what you're trying to do by international mail or email.
If Patrick is hard to connect with even before it's started, how long do you think it will take to get the custom work done?
And consider the possibility he's not a fabricator, but instead orders them from a fabricator. That would mean paying for custom work anyway.