16,8 is too high a voltage. Your harbor freight meter might not be accurate. It is safe to assume you have another vehicle , test that one. 14.7 at the battery would be OK. Then you can determine if your meter is off or the Pantera alt is over charging.
You did not say if you are still running the stock alt or you have up graded.
A loose connection or high resistance in the alt / reg ground circuit can cause strange voltages. Start there rather than throwing parts / money at the problem.
Most major auto parts stores can test the alt if removed from the car. My gut feeling would be more likely around the regulator. The first regulators were mechanical , the later solid state should fit without rewiring. I have no idea when Ford made the switch to solid state.
I would expect a bad alternator to under charge rather than over.
If the alternator was trully bad consider a late model internal regulator in the 100 amp range. That does open the can of worms of up grade the amp meter in the center sub dash. The amp meter handles all the current in the system and can be a fire hazard. There should be plenty of information on this forum on that subject.