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???!!