The Westley Richards action, often referred to as an "Improved Martini" is actually a development of the Peabody action.
In fact, the patent submission was before that of the Martini so really, both the WR and Martini should be referred to as "Improved Peabodys"
The 1871 is similar to the 1869 with a separate pivot for the lever and the hammer. You can see that there are two screws on a '71 and only one on a '69 and '68. Other than that, they are much the same.
I don't know what the internal capacity of the 500No.2 is offhand but Inhave seen Martinis chambered in it so definitely an option on the bigger Martini actions.
I will try 54grs of H4198 and a paper patched or lubed 440gr bullet. That is what works in my Turner and the WR action is surely robust enough to take much more than that. Will report on that when it happens.
Will get better pictures soon. Been cold and snowy here the last couple weeks and my indoor photos never seem to work out well.