I swapped a low mileage 2003 6 speed manual into my 1999 F250 5.4.
What options do I have as far as a heavy/heavier duty clutch set?
I am assuming that all the clutch parts are the same between the
5 speed & 6 speed and also through the years.
Please correct me if I am wrong and point me in the right direction.

 

Not sure what's out there. Centerforce perhaps?

 

Did you get this conversion done? What all issues did you run into? I'm looking at doing the same thing in my 94 F250 7.3. The transmission looks longer and the slave cylinder is different on the 7.3 version.