I guess it was a natural since production shifted to Silao, Mexico for 2001-2002 (U.S. models); they kept making them for Mexico all the way through 2006 I believe.
As far as that tandem axle setup goes, I have my doubts about the rearmost one being a drive axle; it's almost surely there just to add GVWR. There are some weird features about it as well.. the rear hubs look the same as the regular Dana 80 hubs, except there are 4 bolts on the cover instead of 5.. and the wheels appear to use lug bolts instead of studs w/nuts. Also, I can't tell but it looks like there are no shock mounts for the rear axle? All that stuff has me feeling like it was a homemade job, but I've seen ads for several of these Mexico tandem HD's, and that leaf spring mount setup looks factory-made, to me.. although portions of it are bolted to the frame instead of riveted. Hmmmm
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Richard