Pivot Spawn Location To Face Instigator by 90 degree increments

The objective of my game is to mine resources and complete an objective. The world is on a square grid and I wish the mined resources to drop spawn closest to the direction of the instigator in increments of 90 degrees. I currently have the calculation to determine if the Spawn Actor location should be pivoted 0/90/180/270 degrees compared to the forward vector but I can not figure out how to pivot the spawn actor location to face the instigator mining the resources.

Here it shows the items spawning at the forward vector location (green blocks and the 1 empty block). In this image the items are spawning in line with the forward vector and not towards the instigator.

Here is the equation that creates the above image. It is of course without the rotation affecting the spawn location because I can’t figure out how to pivot the spawn location so that it spawns actors towards the instigator.