I've used the DJM stuff on a couple of trucks and it has held up very well. I have their shackles and hangers on my current truck with airbags and I tow quite heavy. I used their front lovering arms on my last truck and they stood up very well to lots of miles and towing. I've never used the McGaughys stuff, so I can't comment on that. Only note I might add to your plan is that on my 3500, I had to remove the upper overload spring and stops to get the rear that low. With the airbags, I've never missed them though.
Edit/P.S. Regarding traction bars . . . I know a lot of guys use the caltracs and are very pleased with them, but those things are prettty expensive as I recall. I built a set for my truck and the total outlay was around $100 in materials plus a couple hours of time. I mainly needed mine to stop axle-wrap and shudder while towing heavy so I didn't build in any anti-squat or anti-dive (they're just "flat). Might be something to consider.