THis is gonna be short, because I have to go to class now.
Make sure you check that the intake and exhuast valves are the same material..should be, but I don't want that on my conscience.
As far as 50K miles, The only parts moving in contact with the others is the cam, roller followers, and the pivot studs. I measured my cams and valves at 49K, and they showed no wear out to 3 decimal places on the micrometer.
The machine shop confirmed all this as well.
If your car was maintenanced well and the measurements are good, I would use all the parts over as long as you use the same cams. There should also be no wear on the valves either.
Just get new ford valve seals.
Later,
warmonger
