How do you figure thats how you measure spring length...
I'm just saying the length with weight isnt a relative point as to whether they are good or not.
They are 2.5in wide pretty damn long leaf springs from a regular non commercial pickup truck. The only thing that will make them shine is how you assemble the pack. The main leaf definately has potential seeing as how 52's can flex pretty well.
My only point is that its a 60inch spring. So your halfway between a 56 and a 64. Build it light (IE less additional springs) and it will flex well. Less springs = more flex but you always have to find the happy medium with support, flexing, axle wrap etc.
I run 56in rears from a regular 3/4ton truck with every other leaf removed.