The most convincing argument I found was by @MARLIN375, for the USDS, near the no.4 cylinder:
forum.ih8mud.com
Please keep us posted. I would like to install one soon as well and need to know if the 11414 will fit in there.
Seizing the opertunity to examine all of the frost plugs close up, I noticed that the #4 cyl. DS hole (behind your fuel filter) is cast slightly prouder than the rest. I removed the plug and fit the heater with the element at 6 oclock (pointing down). I believe that this is exactly where Mr T intended to put this unit. The hole has a larger surface (longer barrel) for the Oring to seat on, the element sits a full 12mm from the cylinder wall (center of the water jacket). It is positioned in the center of the engine for even heating and is not on the hot exhaust side.
Winter is coming - block heater installation
Concrete: I read your original post(s) and chuckled only b/c it sounded like something I would do. I even commented in this thread last year that I should order a spare as mine has been in use since I bought the truck new over 11 years ago (well, winters only). I clearly cursed myself and...

Please keep us posted. I would like to install one soon as well and need to know if the 11414 will fit in there.