Yes, one of the Z car questions for the ages!! First, There isn't just ONE color. What the hell? After almost 50 years of Z cars I've discovered that there is often some variation in the 240 rear panel, hub cap and grille color, yes, and tag light assy, between cars. Light charcoal right up to a fairly dark charcoal. Datsun wasn't at all strict about keeping the color exactly the same throughout the entire 69-73 range of 240s. Why should they? There was a long line of customers with cash burning a hole in their pockets and, more importantly, cars just weren't manufactured to the kind of standards that apply today. I'll give you another example of what I'm talking about. I've seen a lot of 240 air filter housings through the years and I've seen more than a few - from the factory - that didn't have the full compliment of decals. On Tue they ran out of the air filter element replacement schedule decals, what to do!!! Ship em what we got, more decals coming in Thur. No big deal. Back to that hub cap, tail panel and grille color (and TEXTURE) and an example. I have 5 virgin, unused, original wrapping, etc, etc D hubcaps and they are 3 different colors! My point, just don't sweat it too much. As long as the color of your grille, hub caps and tail panels matches and isn't too far from the color of your tag light assy you're good. Now on to the TEXTURE issue. Yes, it should be a bit scratchy/sand papery. How to get that feel. A skilled painter using the right air pressure and distance between gun and object will achieve the right feel.
Slightly different story for 74-78. Some other time.
Now if I can just find that thread about tie down hooks/brackets. I've done some research in the ancient Datsun files and found some interesting info on the subject.