Just wanted to close the loop here, and to thank everyone for their time and input on the matter.

I ended up bringing it to a local bike shop. They went the chemical route, and used lye or something similar to dissolve the stem. The mechanic said it took the better part of three days to complete and that he was very deliberate in his approach, slowly adding chemicals and of course working in a well ventilated space. He said with a slow, deliberate approach, the reaction was not volatile and resulting fumes not excessively caustic. Extreme caution and a lot of patience seems the name of the game. Back on the road and very happy with the results. Thanks again everyone.