I've never swapped an axle, but track width (center of tire tread to center of opposite tire tread) would seem to be a helpful measurement since it can be found in various documents and pertains directly to comparing the width of different stock axles and wheels.

If this measurement is not useful for axle swaps, please explain why. I would like to learn more about this.

1958 1/2 ton rear track width is 61".
http://chevy.oldcarmanualproject.com/chevyresto/58t003.htm

Camaro rear track widths

67-69 (1st gen) 58.9"
http://www.oldride.com/library/1968_chevrolet_camaro.html

70-81 (2nd gen) 60.0"
http://www.oldcarbrochures.com/main.php?g2_itemId=26006

82-92 (3rd gen) 61.6"
http://www.thirdgen.org/rt_october1986_mustang_vs_camaro_irocz

93-02 (4th gen) 60.6"
http://www.motortrend.com/cars/2002/chevrolet/camaro/specifications/index.html

"Nothing astonishes men so much as common sense and plain dealing." - Ralph Waldo Emerson