im running a 1980 1/2 ton rear in my 57, (not sure of the difference in width from your original rear).
i am running 15x7 in the rear with 4.5 back space and 15x6 in the front with 3.5 back space, giving all wheels the same out space.
i too am running front disc brakes.
front and rear tires i am running are 225-70-15. i dont have any room to run anything bigger in the rear unless i want to mini tub the bed.
mine is lowered in front with a 3 inch dropped axle and one small leaf pulled, and in the rear im running lowering shackles and i also pulled 4 of the original 7 leafs out.
you can see from my pics the stance.
leonard
