Spaced,
Re the Sikorsky ABC:
The American Helicopter Society can supply at least 11 reports, of presentations that were made on the ABC in the 70's. I think they are $15 each for members and $20 each for non-members. There is some duplication of information in these reports.
If you want a cursory overview, you might find
Coaxial - Sikorsky ~ S-69 (XH-59) ABC of value. At the least, it's free.