After filing the slot to the correct depth I took the counterweight to my bandsaw and sawed off the remaining portion. Image 2 shows the Left Counterweight after filing and bandsawing. I will say that the bandsaw cut the lead but not nearly as fast as I had hoped. I think it really requires a blade more suitable for wood than metals with fewer teeth per inch. After triming both counterweights in this fashion I discovered that there were some voids in the lead - empty spaces within the counterweight.
Slot Created by Rat Tail File
Left Elevator Counterweight Partially Trimmed
Both Counterweights Trimmed Revealing Voids Within