I got my kit from Little Shop manufacturing and then combined it with a GMT 800 hydroboost from a 2003 Escalade and I swapped the fronts with SBC calipers and rotors. My chevy shops like a BMW now.
Finding the hydroboost pedal from a GMT 400 is the hard part. You need to find a 2500 truck and even most of them didn't have hydroboost.
PS - with respect to the above post, the GMT 400 hydro for rear drums doesn't work for this set up. I found this out the hard way. You will wind up with a mushy pedal that goes to the floor.