First thing I did in my WE4 with Astroroof was install the maplight in place of the dome light.
Fits right in there using the same wiring and two screws and no rivets unlike the factory did, for a more secure mounting (never needed on my car) you would have to add the rear rivets.
Mine went in the stock location just fine, I did it 20 years ago so I'm not sure if I drilled one mounting hole or not to fit the new bracket in place with sheet metal screws.
Minor fabrication and wiring, power and ground, and it covered most of the depression from the stock dome light round bracket but not quite all of it, I rarely looked up at it excepting when turning on the map lights.
Depression in the headliner faded with age and certainly with sagging anyways.
No headliners right now so no good pics. for ya.
And yes if you buy one used make sure you get the whole thing.
I have a GN with the factory astroroof and maplights as well maybe I can get some pics. of both cars for ya since I got this new digital camera for Christmas.
With no headliners I think most of the factory mounting could be pictured if I left it all in there, lights are back in both cars just no headliners.
PS: The dome light isn't quite as good as the larger round one but the maplights are quite bright and work very well.