"I was wondering if anyone could refer me to any resources, either books or on the web, on the action design of a Farquharson single shot?"
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A small series of books have been written about the British single shot falling block rifles, by writer, Walter Winfer, with the first one in the series about the first in that type, a hammer falling block design by the Scottish gunmaker, Alexander Henry. Though, in many respects, it was very similar to the later Farquharson design of John Farquharson, other than that the Farquharson design had internal hammers, while the Henry had an outside hammer design. The Alex. Henry original design was later obviously copied by Steve Earle Wesson during the late 1870s, in what he called his Long Range model. Some posters on some of these forums have said that Alex. Henry copied the Wesson design, but that simply isn't true. Once the Farquharson design patent had expired, other British gun makers made them; the other books in the Winfer series have one book for each of those makers.