Not sure where the freeze plug heaters install from the factory but if you go to any autoparts stores that sell them for your truck the instructions tell you exactly where to put it. The hardest part about installing one is getting your old one out. But its not that hard really.

 

Next to the oil filter. There is a freeze plug there.

 

Yeah, there are 3 freeze plugs on each side of the block. But depending on which heater you buy and how its designed, the instrustions will tell you exactly which one to put it in, which direction to turn the heating element, etc.......