OK update here as I am getting ready to reassembly the motor with a fresh head and new oil cooler seals. I took the part in question (see picture at top of this thread) and tried to see if it came from the OPRV. It slid down the OPVR main tube and fit perfectly in the hole in the bottom. Snug. Now it's down there; I figured it pretty much belonged there because it was a perfect fit. And it didn't seem to want to come out too easily after it got in there (I left it for I didn't have a set of small needle nose pliers to pull it back out) After looking at this image I think it is number 2 in the image. It fits inside what I guess was #4 down inside #6? I never saw part #4, it is still inside #6 which is still screwed in the block.
For reassembly, I have the small piston thingy (part #2) slipped down into part #4 snugly and then the spring goes in over it and I tighten down the cap (#1) after it is all in? I don't want to screw this up but this seems too simple; AKA I don't really understand how this thing does anything :-)