Those are some nice shocks. I know you get a good deal, but take a look at offroaddesign.com, as they have some custom valved shocks set up for these trucks. As far as the length goes, you generally need more droop than stuff. It really depends on how you are going to use the truck. See below link to see how to I measured for the shocks. If you are actually going to use the truck, you probably need extended front shock hoops. I bet that 16" compressed length will only give you 1-3" of up travel. Pay attention if you have a SM465!
http://67-72chevytrucks.com/vboard/s...0+lift+install