Ummm a Ford 9" diff would IMHO be overkill for a strong diff!! Even though you may be putting in a 2L turbo mill with heaps more mid-range torque than what the 18rg, it still would not need a came out with, it is still no brute of a V8 that produces dickloads of torque. Go with something smaller, way smaller! Also you mentioned about the rear brakes disks Vs drums, its more of a cosmetic thing in a sense that your front brakes are what do the majority of the work, and certainly I personally would not put in a Ford 9" just for the sake of having rear disks!