My truck is lowered 4 inches in the back. ECE says if it is lowered 4 inches or more, then shock mount relocators are highly recommended, to restore the correct shock angle. In my opinion, a 3-inch drop is borderline, so I would recommend it, too.
As for shocks, I installed KYB's on my truck, but only on the rear. With dropped spindles, you can use stock-length shocks. I don't have the part number, but
www.earlyclassic.com will get you the part number and then you can cross it over to another manufacturer, if you like.
Okay, it gives you a part number, but only for a front drop or a rear drop, with coils or with leaves. But, they have an 800 number you can call on Monday and their staff will be glad to help you. They're really nice folks.