I just bought a new 40 gal gas hot water heater that was still in the box (staples still sealed, unopened). I couldn't see any date on the outside of the box, but it did tell me that it was a Sears Power Miser 8. I got the tank home, and looked at the warranty posted on the side of the tank--to my surprise, the hot water heater is a 1979 model, #153.335841. It also says "Prop" on the side of the tank. Does this mean it will only run on propane? Will it run on natural gas (which is what I have)? If it can be hooked up to natural gas, what would your advice be about using this lovely "new" 27 year old dinosaur? I would really appreciate some help/advice on this. Many thanks!