Skhell, you are trying to over complcate things. All you need is a small regulator valve (similar to our needle valves) between the oil supply and the intake manifold between the throtal body(carby) and engine. The vacuum of the engine will pull the oil through. You need the top of oil supply tank to level with the intake point on the manifold or as close as possiable. You require a very small amount of oil to go through the system as all it is for is to lub the valve seats. That is what the lead in the pre unleaded fuel days done. Or you can get a car with an alloy head and then you don't need that oil anyway as it will have stelite seats and hardened valves. Your Toyota motor cars must have different type of engine as out here all Toyota's will take LPG, it is just some thing that the car manifactures don't want as common knowlage. The other thing is mods such as LPG conversion in the new car warranty period will void the warranty.

Cheers