Couple of good write-ups here:
Another owner asked on the FaceBook T1N forum about specific instructions for removing the T1N headliner. There are plenty of later generation videos on YouTube, but he did not find any specific to the first gen. As I'm starting the insulation process, took some pictures. There may be easier...
sprinter-source.com
I know that lots of people have done this; but I have been able to avoid doing it until the snow tore off my antenna. So into my Sprinter manual, and it certainly gave the basics, but also seemed to miss some points. Another good write-up is here...
sprinter-source.com
The screws are all T20, not T9 as in HKPierce's write-up. I think the hardest part is reinstalling the B-pillar trim, as it includes the large buttons for the seat belt height adjustments. It'll help a little to drop both seatbelts to the lowest height before removal. You'll still have to hold the buttons up while placing the sliding seat belt slot at just the right height.
There are 4 plastic clips along the back edge of the headliner that are likely to break when removed. They're Mercedes part A0089880978; I'd order a new set of 4 just in case.