Thanks everyone for the input and suggestions. Local fellow forum member Toytech offered to grace my frame with his Campagnolo BB tap. This seemed like the simplest solution and least likely to cause damage to the threads, so that was my plan A before moving on to other options. Fortunately, that's all that was required. The Campagnolo tap went in without much of a struggle, and the BB is now installed. Whew. Crisis averted.