Cary can help you, there is also enough info kicking around to figure this out. I came across nearly the same deal as you for 03' axles which is why I am not going to do the 05+ swap. Here is a short list of what you will need to do.
-As mentioned above, you will NEED to give Trevor a call at PMF and have him make you an RSK for the from that accommodates for the wider SD spring perches. They are nearly 2 inches wider overall, its too much to pry the springs apart and looks terrible/hack job if you do it this way. Trevor can help..
-You need to buy a track bar bracket and weld to the frame to line up with new longer superduty trackbar. Find the thread by frankthetank and look at the pictures for how this needs to be done- HIs thread is for a 05+ axle swap, but the track bar location/setup will be similar to the 99-04 axles. This is the bracket I am using.
http://www.ruffstuffspecialties.com/catalog/PAN-OUT.html
I believe Cary sells one as well.
-You'll need 8x170 wheels, remember 05+ wheels have very small backspacing and will look funny without the wider 05+axles, and IMO non of the ones from 99-04 are that nice. Aftermarket or whatever, pick your poison but you OBS wheels will not just bolt on.
-(you will also need metric lugnuts. SOme axles are 14x2.0 course thread, some later 02 and up are typically 14x1.5 fine thread) Keep this in mind.
-Your stock steering box and pitman arm will work, but you may have to have the pitman arm reamed out to accept the 99-04 tie rod; this I am not positive on yet, but I know it has to be done for 05+ steering linkage, so maybe/likely for 99-04.
-Are you going to rear superduty springs as well? They use a metric bolt, you can re-use your rear shackle, but will need to clearance it a bit for the SD springs and ream out the hole slightly that accept the through bolt from the leafs, just a bit to take the metric bolt. Spring perches on the rear work just fine (unlike the front) unless the axles are for some reason out of a cab and chassis truck, (unlikely but worth mentioning I guess).
-Unit Bearings are not as bad as everyone says (IMO), they can be had for a semi un-reasonable price on rockauto. Keep this in mind and perhaps throw some fresh ones on unless you know the history of the other ones. Chances are youll have to do it in a few thousand anyways, may as well be on a bench.
-Yoke from your current 10.25 will get you rolling 2x4, may want to attain another somehow so you can sell your 10.25 whole. Not exactly sure on the front driveshaft, as others have mentioned it needs a conversion Ujoint that is commonly available at the local driveshaft shop, but I didnt write the part number down when I read it, now its long done.
-Krause
