I am in a similar boat and would love to have all the measurements to fabricate my own. I did take some measurements from a C4 I have here and figured out that the rear body (in front of the rear tires) will be about 12" off the ground at the rear of my wifes suburban. I would prefer it to be 9-10" and am not sure if I can pull the rear brackets up a bit as I don't fully know how far they hang below the bottom of the frame.
This is from progreesive's site.
Our 1984-87 C4 Kit Tech Data:
11” brake system, clears most 15” Aluminum wheels
58.5” Hub width
Ride Height Data: Center of wheel is 1.5” above the bottom of the frame.
http://www.progressiveautomotive.com...acket-kit.html
hope this helps