To convert a Massey Ferguson tractor from propane to gasoline, you will need to make a few changes. First, you need to install a gasoline carburetor, fuel filter, and possibly a voltage regulator. You will also need to install additional fuel lines to connect the new carburetor and filter to the fuel tank. Then you need to purchase a new spark plug and spark plug wire set for the gasoline engine. Finally, open the gas tank, drain and replace the fuel, and you should be all set.