Thanks Mark for the warning. I appreciate that an unpiloted tap runs the danger of creating threads that will put the cup out of parallel with both the BB and the opposite cup. Fortunately for me the existing threads are in good enough shape that the cups starts properly. there is just a bit of roughness in the outer 3 or 4 threads which I am trying to smooth out a little.
Before receiving Jim's offer of an orphan cup I achieved some success at cleaning out the threads with a sharp steel pick. I shall proceed with caution with the thread chaser that I will make out of the cup that Jim is sending me.
Brent