Edit: After reconsidering all I really need to know is how to attach a header board to the end of cut hardwood planks (so the ends of the hard wood planks will be flat (no tongue or groove)).

If I were you I would leave in the board that is running on the diagonal, and install the other area as if it were it's own room. Trying to weave the new flooring into the existing is pretty tough. It would require removing the header board aka the angled board and staggering each and every row.

Sorry,

In the image the left line of the drawing is the CURRENT end point of the hardwood. I will be removing the header board, weaving new hardwood in, and then creating the diagonal header after I extend the wood out a bit to cover the patio door.

EDIT: Ok, actually, all I really need to know, is how to attach a header board to the cut ends of hard wood planks...Yeah, over complicating what i really needed to know.

Perfect, thats exactly what I needed to know. Thank you very much!