depends what it is,
i am going through engineering for my build at the moment, but its a 2.8 with a big single, half cage, suspension & brake mods.
but
you need to submit the paperwork to DOT and they will respond with approval in principal. then you engage and auto engineer who sorts it all our for you.
http://www.transport.wa.gov.au/mediaFiles/LBU_F_VS_ModificationLightVehicles.pdf