During the Hemi swap, I noticed this deep hole in the driver's side of the block and always wondered what the purpose was. Well, as I was looking into engine block heaters for my JK, I found this on a 2012 Ram (82212497). Looks like you can get it anywhere between 85-100 bucks.
Straight forward install, pull the starter and bolts right in. Comes with a harness that is plenty long to get out to the front bumper.