[Captainfab]

From what I can see this is what I think you have. The frame and rear springs are original. If the rear differential is a 10 bolt, it is not original and likely the mater to the front. The front differential is a '79-'91 Corporate 10 bolt. The front springs are likely from the same year and application as the front differential. However the front spring hangers appear to be original but I don't know how the later model springs are mounted to them. The original springs and the '79-'91 springs have a completely different spring pin and bushing assembly. Hopefully I am wrong about the spring hanger. What you likely need are 4" lift springs for a '73-'87 K10.