Getting ready to swap a 5.7 into my 73 Dart Swinger

Help!!! Im running out of spare parts haha
However above the starter there is a slot into the block with one single bolt that secures some kind of flange... I thought it was for the knock sensor but just dug those out of a box and installed them still no sign of the part that goes to the block just above the starter!!??? What am i missing???!!
Heads up guy, mine needed two knock sensors not just one. And a small ignition filter attached to the back of both heads. Without them I got no love. Mine is a 2010 6.1 tho so may not even be relative? Love your progress. It is not for the faint of heart for sure! Well done good Sir!