No engineers report needed unless you start modifying the body or brakes. HJ's are still a carry over from the HQ 350. You just need to show the engine is not earlier than the ADR rules for that on the vin plate and get a blue slip. Have a look at the regs in your local state road authority first. It gives details on engine size and weights and mods that can be carried out without an engineers report. Easy mod fitting a 350 in a HJ, buy the correct engine mounts and basically only minor redirection of a couple of thing and your done.