This could be John Barrow’s tombstone in St. Martin’s Garden. Prominent “B” in the 2nd line center, size is right for the side wall of a box-style monument. If the collapsed monument base photographed by Regina Koellner is indeed Barrow’s, they might have set the surviving written slab up like this after the collapse, rather than leave it laying on the ground. Notably the bottom two corners were broken from some collapse. Also notably, this is the only tombstone that they affixed up on the wall; everything else is just laying about. I can’t crack a single word or date on it though, just that letter “B” and a few other strays. Maybe the “U” lower down is for Ulverstone. There are six lines, the 1st and 3rd are italic, 1st is likely to just be “In Memorium” etc.