Level of difficulty changing 8 3/4 gearing

In terms of difficulty, it's more of a 4ish. In terms of special tools, I'd call it more of an 8 because there's things like the dial indicator, and rotating torque wrench, and either the pinion depth tool or a set of checking bearings, plus the bearing pullers and press, that make it more complicated. If you've never changed the ring and pinion, I'd advise to pay to have it done, or buy a complete center section unless you plan to invest in some tools and have shop air. Swapping the chucks is easy enough.