I was tipped off to this site,
Reel Radio by the owner of LunaDisc in Alexandria. It streams airchecks and home recordings of actual top 40 radio stations broadcasts from the 60s and 70s.
Just listen to Tiger Bob Raliegh's show on WPGC,yes that WPGC, to hear the variety of the Top 40 of the time. Unlike an current top 40 station. Just to name a few to be heard in the two hour air check... Strawberry Alarm Clock, The Byrds, Fifth Dimension, Stevie Wonder, CCR, Wilson Pickett, Grass Roots, Tom Jones
, and a song which would be politically incorrect today... The news and ads from the time are worth hearing as well!