What are those "shims" from? I left the thrust washers (that go behind the side gears) in the first time and ended up with a spool, leave them out.
On another note, install goes way smoother if you can pre-compress the unit before putting it back in the carrier (like they are originally shipped.) You can just use a piece of all thread with washers and a nut on each side to draw it back down if you don't have the original hardware.