Pill Priory - by John 'Warwick' Smith, 1787 (view from the North West) - Courtesy of Ian Bannister (Milford haven)
Pill Priory by Taylor (late 18th Century) - View from the East
Pill Priory by Henry Gastineau 1791-1876 - View from the East
Also, a book by Gregory Sharpe called "A second argument in defence of Christianity - .pdf 13.5MB - digitised by Google " which was published in London, 1762 illustrates Pill Priory on the fore-edge/fanned to the right on the book (shown below).
The Department of Rare Books & Manuscripts, and Special Collections at the Boston Public Library, USA, where there is a copy of this book and where the picture on the right edge has been found, were thinking of digitising the book. However and on closer observation, they stepped away from this as the Rare Books Conservator thought that the binding is too fragile to withstand the rigor's of digitisation.
The only reason they can think of that their library has a copy of the book with fore-edge painting is that fore-edge paintings were commissioned by individual owners. That is, fore-edges were not mass produced but done at the whim and vanity of the book owner. They just happen to have that particular book. Around 1941 a collector named Albert Henry Wiggin donated his vast array of books and prints to the library. At some point Mr. Wiggin must have acquired this volume for his collection. They have no inclination as to why this painting was/could have been used. Neither are there any references with regards to Pill Priory in this book.
Another copy of the book has now been digitised by the Oxford University on 9th July 2008 - totaling 80 pages. Also, copies of the book (5 volumes) are in the library of Cambridge University, the University of Sheffield and the University of Wales, Lampeter and it is also available from a UK book seller (2008). However, none of them have fore-edge paintings on them.