MACV/SOG is fairly well-covered by John Plaster's book and (in a more scholarly manner) by Shultz's The Secret War Against Hanoi. Wikipedia also has a decent overview here. Wilf has done some digging on them, as have I in the course of my studies. They ran recon in more isolated corners of South Vietnam, but their main focus was on the "denied areas" in Laos, Cambodia, and even parts of North Vietnam. Teams were typically a mix of US and indigenous personnel (3 US and 4+ Montagnards or Nungs with some SVN at times).