OEM Track Width

[240RR]

OK....I am using rear suspension from a 350Z and need to figure out how Nissan or OEM measures track width. I always thought it was flange to flange (outside) but appears it may be a center of the tire measurement.
If I can not find out without a doubt I may have to hijack a 350z and get some measurements as this is critical to my chassis build.
OEM specs state rear track width on a 350z as 1539mm
Thanks!

[70rs]

As I understand TRACK WIDTH.....that should be outside tires edge to edge with OEM selected tires in place. I could be wrong, wouldn't be the first time. :D

[240RR]

As I understand TRACK WIDTH.....that should be outside tires edge to edge with OEM selected tires in place. I could be wrong, wouldn't be the first time. :D

Oh, I have seen that mentioned also. I might have to just find one to measure so I can make sure. Funny when I do a Google you get three different options. :(