Can anyone recommend a source, or sources, for solid info on the history of spey casting? I'd love to learn more about greenheart rods, the scottish origins, scandinavian innovations and the technique's leap to north america.
at least the last three parts of your question could be more difficult and controversial than history of politics.
There is no special literature I know, covering all that. The different sources for those parts, at least the ones I got access to over a longer time, were all different in some aspects, depending on their origin.
It didnít get less controversial since GŲran Andersson was invited to cross the Atlantic to show his Underhand technique with short shooting heads, with all further developments since then; not only in the U.S.A., also from his own scholars in Scandinavia and others in Scandinavia and UK, going different ways with different approaches.
What we have nowadays is a big mixture of techniques and styles with different origins. And it seems to be, every direction involved is claiming more percentages than in sum 100% can offer for all together...
See alone the differences in terms to describe the techniques and styles.
It depends on how deep you want to dive in.
For an objective first orientation I would trust Simon Gawesworth in the U.S.A., with Scottish origin, as long as the Scandinavian innovations find consideration as a very big part, what they disservice.
As a Bavarian I can be very relaxed to all this. I enjoy all the mixtures of nowadays, no matter how they are called and where they come from.
Good luck !