Help Me Figure This Out

['76 Big Block]

I replaced the front springs with new coil springs to lower front 2".
Then, I replaced the rear shackles that were to lower the rear end an equal amount.....
And this is where things went south.Now, my truck sits really funny----the passenger side is noticeably low---almost as if it had a flat tire, compared to the rest of the truck----I don't know if the spring on the driver's side is not seated, or what's going on, but it definitely isn't sitting even in the front.
I also haven't been able to get my head around the fact that the shackles that were supposed to bring the back down are actually longer than the ones I took out----can someone explain this?
Any help would be appreciated----thanks in advance!