WGI is 36' to 48' with the average at 48' (so basically the vast majority is 36'). Of course that figure is pretty irrelevant because turn 1 is more like 150' wide these days.
It's easily 4 lanes though, it just seems narrow because of how close the guard rails are.
Mosport is wide enough to go 5 wide, the pit entry is the narrowest area if anything.
Road Atlanta being 40' comes from the satellite images by the way, and it's clearly 5 car widths.
As far as the front stretch goes, the inside pit lane wasn't there until after its last major renovation when they widened it to modern standards.
The Brands Indy circuit is quite wide and much more modern in terms of catch fences and the like.
It's when you hit the GP loop and a series of 4th-5th gear corners things get hairy.
There's been some really scary crashes on that part of the track so the prospect of an LMP tripping over a GT car like we've seen at the Dunlop esses, Porsche curves, or Farm curve at Silverstone is quite worrying.
https://www.youtube.com/watch?v=FJ5lZutPcfA
That's just GT3 on GT4.