The Spurs might have been AA. A clue to who they were farm for...I remember seeing Don Baylor play for them when I was about 10 years old. He was drafted in 67 by the Orioles.
You were right on the money!
Class-level: AA
Major league affiliations:
Baltimore Orioles (1969-71)
Houston Astros (1968), Chicago Cubs (1965-7)
More interesting reading here:
http://en.wikipedia.org/wiki/Dallas-Fort_Worth_Spurs