You folks are over-thinking this.
On a flat driveway, concrete, tar, or parking lot;
Use a plumb bob or level to mark the driveway under the center of the REAR bumper (or trailer hitch). point A
Use a plumb bob or level to mark the driveway under the center of the FRONT bumper (or center between headlights). point B
Now strike a line or lay string from point A to point B, stretching beyond the two points.
Your rear tires should measure from the line to center of tread, or outside of tread equally left and right (unless your rear springs are bent).
Your front tires should measure from the line to center of tread, or outside of tread equally left and right (unless your track bar is off).
How important is this, not much for a trail rig.
I had to use a cargo strap to pull my axle over to reach the track bar after putting coil spacers on the front.
So my track bar is about an inch too short tight now, with only minor shaking at highway speed.