Not to sound like too much of an ass but..... if you have questions about Alcan springs, you should probably call them.
It's probably safe to say you meant to ask about what we can do with our springs and we can put 1.5" on both ends if you like. That bigger eye requires a good bit longer shackle to keep the spring from hitting the frame which is why we generally stick with the smaller rear eye. We already stretch the shackle 1/2" just to make the factory smaller eye size work, you technically need 3/16" longer to clear the extra diameter which isn't bad but the frame also starts dropping in this area too which messes it all up. Trying a 5" shackle is probably in the ballpark and it might even take a little more, especially on a K30 where the frame drops deeper.
A lot times front 52s get 1.5" rear eyes from us because the guy built the shackle system around the stock rear spring before he killed them so keeping the bigger eye is just fine.
We don't see giant jumps in durability with the larger bushing there. It seems like all the bushings crap out often if you're 'wheeling the truck no matter what you do, they just get worked really hard. The bigger bolt isn't trivial but our 1/2" bolts hold up pretty well. That's about all there is to it.
