The only company I have found that does a nationally approved GVM upgrade to 3505kg on the coil GU wagons is Pedders. I am having this done prior to first rego, though I think it can be done post rego, but may require further engineers inspection? I rang all the major suspension companies over here and it seems there has been a bit of a crackdown since December in WA on anyone supplying an upgrade over the factory axle limits. I found a couple who would do an upgrade to 3300kg post rego, but the cost was similar to the Pedders upgrade and did not include coil tower braces or rear diff lamination. While I have been no fan of the Pedders gear in the past, I have no first hand experience with it and it seems my hands are tied if I want the GVM upgrade to 3505kg.
Total cost is around $4464.00, this includes the diff and tower bracing, adjustable drag link and offset camber bushes (rubber)and I also need to change mine from a 7 seater to a 5 seater as that is what the kit is approved for nationally. I've attached a PDF from Pedders regarding the upgrade. PED 3190G Nissan GU Patrol GVM Flyer FINAL.PDF