I ran across a slim volume once entitled “The Stone Skeleton – Structural Engineering of Masonry Architecture” by Jacques Heyman, Cambridge University Press, 1995. You might be able to get it from Amazon. It gets into the theory of load transfer for unreinforced masonry, but its focus is mostly monumental structures. I’ve come across articles on this stuff in the literature, but mostly in the context of masonry arches. You might want to go on the Internet and try to locate some expertise in Scotland. I was in Glasgow a few years back and was stunned by the amount of high quality, stone masonry buildings there. It is probably more art than science, but that’s where I would start looking.
This could be a really interesting, but probably expensive, project. I once reviewed some old drawings for the dimension stone work on Wacker Drive in Chicago. Every stone was numbered, and the detailing was phenomenal. My biggest concern would be transverse stability. Maybe you could drill the stuff and prestress the walls to improve capacity. Good luck.
720 3rd Avenue, Suite 1200
Seattle, WA 98104-1820
206 505 3400 Ext 126
206 505 3406 (Fax)