I've got a 2002 with an aluminum drive shaft as well and the shop is telling me that the u-joints the local Ford parts dept. sold them don't fit.
The shaft eng # is 1L54-4602-JC. Is that the same part # for yours? If so, are you saying they actually need U-joints for a 93-99 Ranger?
Ok, just in case anyone else runs into this problem, here is what I've found out.
If you do a search for a 4.0L 2002 Ranger u-joint, the Ford dealership is going to sell you one that might not fit. In addition, if you do a search at Summit or some other place for those u-joints, they're going to send you a 1330-series Spicer...that isn't going to fit either.
The u-joints on a 4" aluminum driveshaft from a 4.0L 4x4 Supercab 2002 Ranger are Spicer 1310 series, with a 3.218 width and a 1.062 cap diameter, at both the transfer case and the differential.
Why did Ford do this? A search for the engineering # on my driveshaft even shows that driveshaft has 'no serviceable parts, must order entire 4602 assembly.'
Hopefully the next person that runs into this problem can benefit from the fun I've been through.