Get "Polygon" Points of Isometric Camera Projection at ground plane?

I am trying to figure out where the cameras frustum is when it passes through the global.y = 0 position when dealing with an isometric (orthographic at 45 degree inclination and rotation) projection.

Kinda been struggling with this.

The end goal is to use the separate axis theory to figure out how far I need to offset the camera to ensure the target is inside the frustum by at least half of its boundingBox size from all edges of the viewport. With the assumption that the bb is a cube.

Here is a diagram is that helps anyone visualize what I am trying to do.

Offset distance should actually read “Offset Vector” and it would just want the shortest offset vector so the second diagram is a little misleading. It would make more sense if it was in the top left of the cameras view.

At this point I have gone through quite a few ideas and still am missing the mark.