Hi!
All that goes there is a plug. No one really seems to know what the purpose of the plug/hole is.
Check out the
www.ih8mud.com board. There are lots of threads, some with pictures.
Here is one to start with;
http://forum.ih8mud.com/40-55-series...head-plug.html.
They call it a "Galley Plug". Most people tap the hole and thread a bolt with JB Weld on it in it's place.
If you are out wheeling and it blows, you are screwed! Most people realize it blew out when their engine seizes up.
Good that you found it before that happened!!!
Good luck!
Bill