I decided to do a little research on the carrier issue. They are indeed listed as 2 different carriers
The 3.27 (LT) carrier GM p/n 92230616 list price $221.30
The 2.92 (2LS) carrier GM p/n 22759584 list price $590.00
If you wanted to just add the 3.55 gears to your car, just buy the LT carrier, it fit will your car. GM parts direct lists the LT carrier for $129. I could probably get it from my dealer parts dept for $160 something. Then you can buy my brand new set of 3.55's on the classifieds.

Cheaper than an SS rear end swap.