Your question raises a few others...........

-Have you yourself yet done this install?

-What extraordinary forces are at play that you imagine might require through bolts?

-Why is it assumed our tapped holes are somehow "shoddy"?

-Why does Ford use thread forming screws for this installation when they add this to a chassis? (FWIW the spare tire under mount is held in place with those type screws.)

-Has anyone's tapped holes failed so far?

Fact is the frame mounted bracket could be safely held in place with just two 5/16" or 3/8" bolts, both in the vertical plane, grade #2 at that. I suppose it could be argued welding the frame bracket makes more sense?

As an aside most likely Ford uses three fasteners more for proper location and parts alignment during manufacturing rather than any safety concern.

Reading those posts where through bolts are used---such as Andrew's original post for example---show the process of placing and holding them while securing nuts is a bit of a hassle. Properly tapping the existing holes requires only the simple process of installing and tightening one bolt per hole, lock washer or Loc-Tite optional.

In the end this becomes nothing more than a personal choice, no one way is better or less safe than the other---assuming things are done properly. I believe anyone who'd tap such holes understands how to do it competently so I wouldn't be a bit scared of their installation.

Does that answer the question?