I have a similar problem. I would definetly check the crank seals like everyone says, but if she is smokeing out the back it is probally something else. I had leaky crank seals (on both ends) and that elimated the smoke under the hood. Oil was dripping on to the cat.
But my burning problem continues. When the engine is cold, and sometimes when I wind it out, or come to a stop after cruzing down the highway at 65, it will leave a cloud of blue smoke. I believe the problem is valve seals, and plan on replaceing them if a few weeks. I did a leak down and compression test to see if it was a craked ring, but all was good. I will let ya know if the seals fix it.
Later,
Adam
91 sho