I found this page when looking for info on the rear in my 1969 T50: https://www.chevyc60.com/the_rear_axle_page.htm

It does not list width's but there is a lot of gear info there.

My truck has what I understand is a GM H170, I could measure it if it would help. The option list includes 20,800 lb springs, I don't know what that means regarding the axle rating. The GVW on the VIN plate is 19,500 lbs.

Mac :{)

1962 K10 short step side, much modified for rally
1969 T50 fire truck, almost nos, needs a few things