I know there is no known answer to this, but I wonder how many 69 Road Runners came factory with the N96 Option. Finding an OEM duct work isn't a needle in a haystack, but pretty dang close, I think.
From what I can find, they made 78,906 Road Runners in total in 1969.
1,412 were the A12 so they all had it.
787 were Hemi's so they all had it. (Of which 10 were verts, I'm drooling as I type)
So if you take those out of the equation that leave's 76,717 cars.
Based on my unscientific, unsubstantiated and definitely informal research based soley on casual observations then adjusted for my own amusement, I'm guessing that 5% of the remaining cars had the N96 option or 3830 cars.
I think the "383" portion is a nice number, so I'm going with that.
disclaimer: This is a total guess which is very likely and completely inaccurate. To be clear, do not quote this as factual information as the number is posted for amusement purposes only.