Rather than spend money on encyclopaedias maybe listen to a few of the excellent Comic Geek Speak podcast spotlights where they go into great detail about the development of key characters run by run.
Give their great Fantastic Four spotlight series a listen and see what you think. Here are the Silver Age links:
Spotlight on the Fantastic Four in the Silver Age Part One
Spotlight on the Fantastic Four in the Silver Age Part Two
That is over four hours of chat and information to guide you through an unparalleled era of MU world building.