The springs are for the front, 4" lift, with the pin moved forward 1" for tire clearance. They're made to give a soft ride. I'm asking $150 for them, without bushings.
The third member is out of a front axle from an '83 pickup, but it should fit front and rear axles on 79-85. The gearing is 4.38. I'll throw in an extra carrier (pictured) for $75.
I'm in Pasadena, on the north end of L.A. I'll ship anywhere if you take care of the hassle by shipping me a box with appropriate postage.