A VX LPG system won't be a straight swap into a VT. The VT and VX factory LPG systems are different in the way in which the LPG mixtures are controlled. That won't transfer across to a VT and makes it a bit more complicated as, while 'plug and play' conversion kits for VT do exist, the VX specific LPG system isn't it.
In VX the PCM is flash programmed with software specific to LPG, with both LPG and petrol mixtures controlled through the PCM. VT require a stand alone controller for LPG mixture control. There are a few around that can be used. The VT factory conversion uses an Impco Adaptive Digital Processor (ADP), which has a self learning capability.
One simpler (cheaper) controller is the Impco Commander which does nothing more than chase stoichiometric mixtures (no self learn).
If you can acquire a VT LPG harness and ADP it's still plug and play. The Commander or other controller will require different, maybe bespoke, wiring (it's not difficult though).
Also search online for 'Apexus'. They do a VT LPG controller and MemCal and have a downloadable pdf on the associated wiring.
With a VT, you'll want an LPG MemCal for LPG ignition timing (exhaust valve life and efficiency), petrol start and high load valve cooling, and trip computer and anti-theft integration.
The hardware side is otherwise all but the same so you still might want some of the VX parts for a VT conversion. You'll need: The (in date) tank, mixer, converter and associated mounting hardware. The LPG filler valves/connection and note the shape of the required cut out in the body. (Maybe trace it onto paper?) The two lock off valves, including the Smart Lock one (on the tank end?). The LPG specific wiring harnesses (which will be different to VT). The fuel changeover switch. The fuel control valve on the converter. The ducting between the tank and the body that surrounds the lines and filler hose (or pipe?). The flange connection between that duct and the body. Any heat shielding.
You will also need LPG 'diamonds' for the number plates. They have to be metal and riveted on. Many workshops will rivet through the plate and into what is behind it. You might want to ask them not to do that or fit them yourself. (Buying the 'diamonds' may be an issue without an installer's licence.)
While you cannot reuse the Copper lines (nor a high pressure hose to the fill connection) and should not reuse the coolant or LPG vapour hoses, take them because they will help lay out the system. You might take the 'P' clips that secure the line but they are not expensive to buy. You will have to have an installer make up new lines for you and sign off on the system.
DIY, at least for the major components, is possible. It's no more difficult than a stereo install. You do have to comply with the LPG standard (most of which will be covered if you are using the VX parts as they were installed in the VX) and have a licenced operator sign off on it.
Australia and NZ share the same standard for fitting LPG (AS/NZS1425) with some minor differences so that should be the process.
