There are systems available for the Navara and there are vehicle running well on LPG, but some specialists have reported problems getting the gas injection timing correct with the Nissan’s variable valve timing system. One uses a liquid injection system, which has the same injection timing as the Nissan’s petrol system along with the same combustion temperature, and that appears to work well. If you’re going to do it make sure you choose an experienced and competent installer, and perhaps consider the liquid injection option.