I tow a 30 foot 5th wheel camper with my F450 flatbed, and needed to reverse the axles on the suspension of the trailer to get a level tow, and have gone over 20,000 miles that way, with no problems of stability or wandering, and the suspension is doing fine, as are the axles.

About pre '99 duallies. I have a Ford custom built F450, Crew cab, 4X4 Dually, that I specifically ordered from FoMoCo in 1996. They took 6 weeks to build it, with a 7k front axle, and a 10k rear.