The promenade deck on Maury was a little extended in the breadth , increasing the deck area.
Maury's props were changed in 1909 , from 3 bladed to 4 bladed , to lessen the vibrations.
Same changes were brought on Lucy , as the tests were concluding.
this is why the Lusitania's 4 bladed prop on show at Southampton is different from the shipyard's pictures , showing her building.
Also , while I was getting thoroughly into research , it appears that the outer props of Maury were put 15 feet more forward than on Lucy.But I couldn't determinate if maury's outer shafts were put more offset than on Lucy.
From what I could see in my books , the hull lines were also different , the tumblehome on Lucy was a little "rounder" than Maury's.
While deck machinery , steering gear apparatus , pumps & other machinery features are the same , some castings were different , as the rudder blade & the main condensors for example...
The hull test procedures were different at the two shipyards , John brown used a towed basin scale model , while Swan hunter used a electric powered wooden launch.
So , we can assume they were sisters , but they differed a lot from each other.
Hoping you've been helped ,
Laurent