Just actually ordered my 4" dropped axle (also does 3") from Sid at Droppedaxles.com. I will say he very knowledgeable, incredibly helpful, and easy to work with thus the reason behind getting my business. Head over to
http://www.droppedaxles.com/ to check out a guide on the installation of the dropped axle, the parts needed, and even pictures of customer's trucks.
Good luck.