Hi GBF
The Diawl Bach has been one of the most successful stillwater flies in the UK for a number of years now, the amount of variations tells it's own story.
Also buzzers and buzzer tactics have quite an old pedigree now, starting back in the 1960s, a lot of literature on the subject.
I shall post a list of writers and books when I can collect it together.
They should not be too expensive on the second hand market, but are very informative, even the older ones.