Jay Helfert organized an "LA Expo" in 2001, with vendors, tournaments for league players, and an invitational 8-ball event organized by Accu-Stats. (Accu-Stats had no eight ball videos and was getting requests for them.) One of the six players invited to the round-robin was Efren.
One morning I wandered by the Accu-Stats arena and there was Efren, alone, doing what you described -- setting up clusters to work through and landing on each cluster just right. I watched for about half an hour. With all those pool players at the venue, I was the only person watching the GOAT demonstrate his practice method for free.
But this particular drill requires tools most players don't have. Also, I wouldn't call it old school as I had never heard of it before.
This reminds me of a drill or prop bet or exhibition demo that Ralph Greenleaf was said to have played. Put three balls out randomly on the table. Put a coin out as well. Run the three balls leaving the cue ball on (near?) the coin at the end.
I like a similar drill, but there is only one ball and the cue ball is in hand. Go to the coin after pocketing the ball in each of six pockets.