4 inch drop?
 

I am dropping the rear of my truck 4 inches with coils. I have heard different opinions but I want you guys opinions. Can I just put the coils in or do I need a panhard bar and new shock mounts?

4" will require either new shock mounts of shorter shocks. ( you want 60% rod showing when at ride height)

you may be ok with the panhard , but it would be best to check to see if its parallel with the ground and how far it has travleled from that position. at 6" you would definitely need the change. good luck!

How much shorter shocks? What application can I ask for that will fit my 70 stepside?

Bryan

Shock relocators will give a better ride than just using a shorter shock, at 4" drop the shock is at to flat a angle with the ground to perform as designed and the shock relocators allows them to be at the proper angle to function correctly. In regards to needing the adjustable track arm bar you are right on the borderline, the only way to know positivly is install the rear 4" springs on truck with all of body installed so full weight is on suspension then measure the rearend to see if its centered, I find 70% of the time or more that the adjustable bar is required to center rearend properly under the frame on a 4" rear drop. You'll find everything you need here
http://www.gmcpauls.com/lowering_springs_&_parts.htm
GMCPaul