Is you keg made of stainless steel? If so you probably won't have any problems with a funny taste as many cooking surfaces are stainless.
Most fire boxes are constructed from 1/4 to 1/2 inch thick steel for durability. Thinner metals tend to rust and burnout quickly. I’m not sure how stainless would perform under the extreme heat in a fire box. You may consider inserting a thick walled pipe into the keg as the fire box and the keg would serve as ornamental.
Have you tried asking Dave Klose at http://www.bbqpits.com/kloseboard/wwwboard.html
or Ritch from Gator Pits at http://pub44.bravenet.com/forum/show.ph ... 3613&cpv=2
? They build smokers for a living and may be willing to help.
Good Luck, Bob.