i never heard of a factory sunroof option... so my guess is that its aftermarket...... but then again these trucks had some weird configurations so maybe. if it is factory id say its really rare but leaning towards aftermarket.
The sunroof is most definitely aftermarket!
Although it is factory, the tailgate isn't original to the truck either. The embossed tailgate only came on the B2000, which was discontinued after 1987.