When I put a MII 8" under my '77, as far as I could tell, it had the same brake shoes, cylinders and drums as the 6.75 that was in my Pinto and freshly rebuilt. So I merely unbolted the original brakes from the little axle, not breaking open the hydraulics, then pulled it out and bolted the 8" in. The 6.75" brakes bolted on to the 8", so no worries about parking brake cables.
Mike