Welcome to the forum.
The info you seek is probably here.
Page 104 seems to have the front track widths, 108 for the rears.
".....The primary role of the General Motors Upfitter Integration group is to provide technical assistance to the hundreds of upfitters in the field who regularly modify our vehicles for a wide variety of commercial applications. The assistance could be in the form of anything from an electrical schematic, to providing dimensional data, or guidelines for lengthening a frame rail....."
www.gmupfitter.com
Not that is matters to the DMV around here, but a few of us install spacers on the rear, to even out the track width between the front and rear.
Best of luck.