The greasable shackles are supposed to eliminate squeks because you can greas them (they have a hole drilled through the bolt with a grease fitting on the end). I don't like them because I haven't heard my front shackles squek (the new ones plus the old ones that were on there for years) and they make the bolt weaker from the hole drilled in them. The boomerang type look more modern and have a curve to them that is supposed to give some when flexed. I would say that with the shackles and the 2.5" lift you won't have any problems fitting 32's under it, but if you want to go bigger I would go with a 4" lift instead because it is a lot work to replace the springs. I went with the 2" lift, shackles, and 1" body lift and I have 31" mud tires and there is still plenty of room. I have a 4 banger and wanted to stay when it's capabilities.