Motown recording session at Royal Studios?

Again flipping through "The Billboard Book of Number 1 RnB Hits" and saw this entry for Al Green's hit, "You Ought to Be With Me".

"Mitchell's accomplishments with Green did not go unnoticed by the Motown folks. "I knew I hit the sound [I wanted]," Mitchell says, "because after we cut 'Let's Stay Together,' Motown wanted to rent the studio for a week." Motown brought 11 musicians down, but no vocalists. "They were checking how I miked the drums and what have you...They cut a week in here...no voices, just the musicians."

The Mitchell referred to above is Willie Mitchell for those of you who may not know.

Does anyone know anything further about those recorded tracks? There is no time frame mentioned other than it was after "Let's Stay Together" was cut.