Greasable shackles have a grease fitting (zerk) so that you can grease the bushings. The stock (or normal) shackles don't. I think it's a feel good feature, but not really that useful. Oh, get some full-size chevy 2" drop shackles, they will give you two inches of lift to match the front. As long as they look beefy, they'll hold.
And to install the rear shackles, you'll need:
Breaker bar (Or wrench and a long peice of pipe)
21mm socket/wrench
Propane torch (optional, heat helps get the bolts out)
Bottle jack (To force the spring down to fit the shackle back in place)
PB blaster/liquid wrench
Lock-tite
It's pretty straight forward, just do one side at a time. Somebody else might give you more details. I'm too lazy.