That little hole in the top of the removable plate you are talking about is for a metal tool to lift it on and off unless you are talking about that little hole in that tab on the metal plate . This looks exactly like the hole that attaches the grate to the shaker.
I can make you the tool you need to take it on or off hot I just need a photo and measurement of the dip in the top that the tool goes in. Just let me know .
The metal bar or handle you speak of in the photo is to stick in the little damper door during operation and shake the grate without burning your hand I call it a shake down tool.
Your firebrick looks good