General advice: if the engine has a long air intake, as a lot of vans do, you need to fork out for an injected system. (Vapour injection is most commom, I have heard of liquid injection but not sure how available or relative cost). Reason: carburettored systems need to introduce the gas before the airflow meter, so it doesn't muck up the metering. this creates an air intake full of essenitally an explosive gas/air mixture, and the longer the air intake, the bigger the explosion if the car ever backfires. Destroys flap-type airflow meters and air filter boxes. The injected systems are much better if you can afford it. (ours was mostly Gov't subsidised). We do not notice any difference in power or economy compared to petrol with our '91 Tarago. In addition, I am told that Toyota do not design motors for gas, (no hardened valve seats) so you need to add a 'flashlube' system (or equivalent). Go for the electronic dosing version - the vaccuum bottle- drip systems are hopeless - I have had both. Drip systems are hard to calibrate and go out of calibration easily. The driving style affects dose rate also: I set mine up, crossed the Nullabor, and found the bottle almost full at the end; probably because the throttle was open most of the trip - very little manifold vaccuum available. The electronic dosers take a signal from any one of the gas injectors, so the dose rate is proportional to fuel usage.