cpp drop kit vs djm kit

[robzilla]

looking at either kit for my 69 c-10.

http://djmsuspension.com/application...63C10Parts.htm

or

http://www.classicperform.com/Store/...ck/6370BDK.htm

what are the pros or cons to either system?
I've got a 71 gmc1500 that i'm going to use as a donor for the disk brakes and rear end. i know the question has been asked hundreds of times, but i can't seem to find the right thread to answer my questions. one of the questions i have is what parts will i need to switch out from the 71? should i be looking to use as much as possible, and change out the necessary worn parts from the 71?