That's already pretty close. Your new links worked and when I enlarged the images to real size or even bigger, the slot still looks fine. If you want to tighten the entire length of the slot, plain paper is an inexpensive option! Glued in with Titebond the tonal properties should be close to hardwood. Try dry fitting, I guess two pieces (max) of standard laser copy paper should tighten the slot nicely. Notice that the glue will swell the paper a bit so leave some headroom!
Then again, we're really talking about a gap that is barely visible. When you glue the fretboard on, some glue will always seep to the slot. The moisture of the glue will also swell the neck a tiny bit, tightening it even more. And finally you'll have to put some tension to the rod to prevent the it rattling against the other half of itself! That alone will keep the rod from moving in a rattling way. And yes, if you didn't already know it, you should always put tension on the truss rod even if the action is perfect. Otherwise the flat bar will rattle against the round bar and the bottom of the fretboard.
So, my advice is simple: Do nothing. It's close to perfect!