I had an 8" on this truck -
Was a solid kit, no worries about it breaking... but it rode very rough. Could have been the cheaper shocks, but this thing could rip out your kidneys.
Just helped a buddy of mine put his into the same style truck with with the 7.3 and his rides rough too.
I paid $2000 to a local shop for the 8" all spring and installation. I was pleased with the results, it was exactly what I wanted, but it rode rough. Put 500-1000lbs in the bed and it will ride great
Just make sure you put some tires under it. Had to drive it like this for a day because my lugnuts were in the mail.