Mr Gasket used to sell shock extender brackets that would bolt to the bottom of the shocks. Maybe they still do...
And I never worry about the part numbers, as long as you know they are a matched set the spring with more leafs is intended for the right side, the pass side of the car, so it counteracts torque steer. A stiffer spring on the right will counteract a cars tendency to pick up the left side of the vehicle upon a hard launch, so the car launches level. Just like cars with factory rear coils put an air bag in the right side of the car for the same reason.