I'm not sure I'd stack 3" springs on top of your 2.5" main springs...it might work, but I wouldn't do it.
Can you just take the spring hangers off the donor truck and move the whole works onto your truck? That might be the easiest way to go...don't forget to get the helper spring frame hardware while you're there. On second thought have the salvage yard cut the donor truck frame and take the entire back half of the truck home. That way you'll have a template for all the needed holes and transfer the axle and springs onto your truck as a unit.
Mike B
