Well, good luck with the HR! They were well made mh's! Not good to run the water pump dry, so I would put a little water in the tank thru the oustside fill, and turn the pump back on, it will pulse as it builds up pressure, then, if no leaks, will shut off, till you turn on the sink, then you will hear it pulse to keep up with the demand. You need to check the water heater, to make sure it is not in bypass mode, the valves should be behind the heater, and fill it up to. When filling it up open the pressure relief valve, till water comes out then close it, and turn off the pump! If all the hot water lines are capped off, that tells me the WH is probably bad, but you never know till you try it? The exhaust leak sounds like a doughnut gasket, between the manifold and the Y pipe? Keep your fingers crossed! It could be a cracked manifold? (hope not!) The overheating, losing 2 gallons of water could just be a stuck thermostat, as you said, or the radiator hoses or just a small leak. You did not say how long it had been sitting? I would also check the brakes, lines, and all things rubber! Is this beast a 460 cu in or a 351 cu in? Glad you got it home, or close to home anyway! Have fun! Keep us posted! Rail!