adapting an existing steam engine is the only thing you've said that makes sense. and its very possible. however the steam engine doesn't actually need a transmission. the steam engine makes enough torque you have no need of torque multiplication, and since they can turn backwards as well as forwards reverse isn't an issue either. if its a 4x4 you would want to mate it to the transfercase otherwise the most efficient setup is no driveshaft and attach your steam motor directly onto the differential. in WWII they started out using steam powered torpedos with a really cool radial piston setup. they used 100 percent pure alcohol to heat the water to steam the entire engine fit into a 18 inch torpedo. it would be a really good engine if you could find an old surplus of some kind, or do a lil web searching. if you can beat the fuel issue you have decent chance, but you have to understand water is not the fuel. the fuel is the stuff that heats the water. so if the fuel is the electricity in the batteries it can't possibly use the alternator to recharge itself. it would be like running your exhaust pipe back into the gas tank and expecting it to refill itself. perpetual motion hasn't worked for anyone in 10,000 years yet, not even once