Dome Light - Need measurements to cut hole in room

[Wgesnerjr]

My Custom Deluxe (i.e. Nothing Custom or Deluxe about it) was born sans an interior dome light. LMC was kind enough to carry the housing, lens and wiring; but neglected to give measurement for those of us not lucky enough to choose a Silverado.

So, could anyone give me some measurements on the hole for the dome light? The housing is curved to match the ceiling, but how far up from the back window does it go? Also I'm not sure how to find dead center from side to side.

Here are some pictures

[TKCR]

Are you going to put a headliner in? Because they are meant to be in the headliner, not cut into the roof metal. Or at least, not that I have seen.

[Wgesnerjr]

Yes, plan on a headliner but the back of the housing has an area to snap in the terminals. Once done, these terminals will hit the body if there is not some kind of hole for it to recess into. Can anyone verify?

[Gmc.guy]

Does this help? I'm not sure what year yours is but this one is a 74 might be same on 73-87 but I can't remember. Maybe putting the headliner in and tracing the hole for cut out will work better ?

[Gmc.guy]

Whoops. Upside down. The hole beside tape measure is centre hole for factory headliner trim. Is the light you bought a factory replacement ? Looks different mounting holes

[Gmc.guy]

Find center on the bottom of the window, corner to corner and use a square to find center on the top? Might work