My brother and his wife live in my parents house now and they still have the original water heater. can't remember the name off hand but it is an electric heater and was originally on an off peak meter. He had the electrical panel redone and they the electric company took out the off peak meter so now its on standard electric rates. As a kid i remember looking at it and thought it was odd that it said rock lined. It must be a heavy unit. by the way I think it is going on about 60 - 61 years old now. My dad used to clean the drainage pipes out of the house once or twice a year by attaching a hose to the drain cleanout and running that down through the pipes to clean them out. They just don't make them like that anymore.
Jon
Jon