I measured the arch of the springs, pretty much used a string from eye to eye, and measures from the bottom of the leaf pack to the string. It came out to be 1ft 1"

I have the feeling with these springs and slightly loger shackles you will not have any sagging rear end issues. Keep in mind these measurements are on a brand new unloaded spring thats never seen the weight of the truck. According to the site they will sag approx 1" over time, which is standard for most springs.
It is also 56" long. 

Luke