The "after" photo.
To obtain the finished product in the photo, I used aluminum polish to buff up the threads to a nice smooth finish. This was done using strong string that would fit between the threads of the exhaust stub. By applying a dab of polish to the threads and then wrapping the string around the stub, I was able to polish the stub up easily by sliding the string back and forth. The exhaust collar had to be polished manually. Overkill? Maybe, but then you don't hear me complaining about a seized or stripped exhaust stub due to years of neglect.