For short periods of time, prescription medications (such as narcotic pain medications or muscle relaxants) may be helpful to alleviate pain or related complications.
It can take anywhere from 4-10 hrs. now if your head gasket is warped you will have to take it to have it milled that takes from 1 day to several days. if not you can just buy a completely new one that fits perfectly for about $150.
I just had a leaking power vent gas water heater replaced after a month short of 10 years. It's a rental. I asked the tech if they should last longer than that and he said 6-10 years is normal in a hard water area like mine. installed a 30 gallon fast recovery gas water heater with a standing pilot 30 yrs ago, my son lives there now and its still operating. This is a Sears/Kenmore model. I also replaced a boiler at the same time and that needed new burners because it did not have a standing pilot.