Dorman Products makes a spark plug rethread kit that will get you out of this situation relatively inexpensively.
Dorman # 42025
Also available at your local NAPA store in the Balkamp/OE Solutions product line under part # OES 6003248. (Sells for $83.49 CDN here in the Calgary area)
Just to clarify the fact that there are two diiferent types of plugs used on Triton engines, depending on the year of the vehicle.
The plug that fits YOUR year/make/model is what I would term a "conventional" spark plug.
I'm an NGK fan, so the PN for a platinum plug is 3403
This Dorman kit uses an extended spark plug similar in design
to the newer (i.e.2005) Triton engines.
For these engines I actually recommend the Champion "Truck Plug" because it is a one-piece design, that eliminates that broken chunk that gets left behind problem referred to earlier in this thread.
If / when you decide to replace the rest of these plugs, make sure you spray them with copious amounts of the best penetrating fluid that you can get your hands on, and let them soak overnight. CAREFULLY remove the old plugs, and inspect the threads to see if they are pulling aluminum out of the heads. Use anti-seize on the new plugs to prevent galvanic corrosion.
Here's a video:
Best of luck, and hope this helps!