I did view the diagram when I was looking at your specific model engine but on mine the diagram doesn't show up. I did a visual on my actual engine and I can't see why I'd need the part since the drain nut is actually located at the end of the drain tube. It would make sense to need that part if the flow control was located on the block. Maybe I'm missing something here, I don't know. And yes, I plan on adding the oil cooler.
Try comparing the two models and see if you can get the valve assem. to show. Compare the FH721V-DS22 and FH721V-DS25.