which leaf springs?

I am trying to find out the right part number for the Super Stock Leaf springs for a 1972 Plymouth Duster. there is one set rated at 2800lbs and another set 3000-3200lbs. would there be a big difference between the two? i dont know the weight of the car but it is an all steel car with a 383 and a gutted interior and 6 point cage. i guess 3200lbs?