Makes no difference to me how or why they rated as they are. Rear axle rating is 7,000, front is 6,000#. Gross weight rating is 12,300#. Firestone tire rating is 3640#. The truck empty is 5100# front axle, and 3200# rear axle. Looking at the CAT ticket: my "heavy" scale weight was 5540# front, 7120# rear. So I was over the rear axle a little, right at the tire rating, and over GWR. I drained off some water and hit 7,000 rear axle and continued on.
I've got a BigWig that might fit the dually, my Curt front receiver hitch might fit, and the Torklift tiedowns I'm not sure about.
I should have bought a dually 2 trucks back but I didn't see myself getting a cabover then.