They were using a Tanner package that had the “Summer gold weekend on WLS' ; Tanners jings
ended with the calls accapella mostly; Additionally; there was “summer sounds best on WLS”
this one and the one you posted sound like they were Pams, they played these over and over all summer for years.
There was one from Jam- “Chicago's summer Fav'rit” 1979(?)
Summer Sounds best was on 1976 “Windy” custom,
Summer Gold Weekend on the Sundance “LS” 1975 package. Jams' AM package had a Summer Gold Weekend, plus JAM had Chicago's Summer Fav & Summer Rock & Roll from Music Jam/Dance to the Music… but these “Spirit of Summer” are a complete mystery.
It sure sounds like Marv Shaw (of PAMS fame) singing lead. He had moved to Memphis in the mid-1970's and was Tanner's staff vocal group leader during that time. Another vote for Tanner.
There's a lot of Tanner stuff we just haven't gotten to yet. The later stuff is all DBX encoded… and all leadered (with dried out leader tape). It will take years to put the reels back together so they can be dubbed.