A couple suggestions I have.First,I would go 3/4t.The`68 front springs won`t swap with the`71(`69-up).You could do the small(2 or 2 1/2")shackle-flip and not change anything with the rear springs.Either get add-a-leafs or 2"lift(HD-type)springs for front.Or,go to a spring shop and get it exactly how you want.For tires you could run 285/75x16s on those 8" wheels.I have this set-up currently on a truck with about 2" of spring work.Use a super-HD tranny cooler and maybe a temp guage.I have one in the blank(vac)hole in the dash.There`s also deep pans for capacity.I had no problem getting parts for my Eaton rear.The closed knuckle doesn`t turn as tight,but you could live with it.Here`s what the wheels/tires/lift looks like:
