I remember putting a Sanyo AM/FM/Cassette stereo in a '65 Mustang (the steel dash had already been drilled). Jensen Triax 6x9s in back and the smaller rounds up in the front kick panels. My dad borrowed the car to run an errand and came back asking me all about the components (!!). Dad was *not* a car-modifier, at all. A month or two later, the '72 Country Squire had a similar stereo system installed. I was amazed. Of course, Dad chilled-out in traffic by listening to classical music - after he figured out how to dub his LPs to the tapes. :-)
Those Jensen speakers were pretty commonplace - and moderately priced, but they did a really good job given the acoustics of the cars back then.