Hey there,
I am not sure if you ever found the answer to your question (if you did please let me know I would love to know).
I have a few suggestions for you.

1. Try to find or attend Albert Torres’s lecture on the History of Salsa. He tends to do it at almost all the congresses he is at.
2. Check out this PBS documentary, parts 1&2 cover salsa and what was before. http://video.pbs.org/program/1253189365/
3. Let me know what you find or if this helps. Here is my blog.
http://salsame.tumblr.com/

Best of luck