Hey there
That particular Mainwaring medal referenced (Hennin 472) is actually a different medal. I recall reading some old numismatist journals that reference the particular medal I have as Mossop... while most of his medals would be signed with his full last name, there are at least a couple of medals attributed to Mossop that have as their subjects French Revolution relatd themes and are signed "WM". (http://books.google.com/books?id=7-8SJCqtsEwC&pg=PA90&lpg=PA90&dq=mossop+medal+louis+xvi&source=bl&ots=hI1P_trGg3&sig=xJ4SmYYnZSEAmmtcudHeFh2T7es&hl=en&sa=X&ei=-0e9UPStEIqTyQH8uoFQ&ved=0CDYQ6AEwAQ#v=onepage&q=mossop%20medal%20louis%20xvi&f=false)
Attached are the images. As you can see, it is in rough shape but I got it for a really good price. For reference, this is what the original Loos coin would have looked like: http://www.acsearch.info/ext_image.html?id=139225
Anyway, this is what I have... the sources I saw were rather old and I have no trouble at all with this being a Mainwaring medal.