Have not seen this 3 ball break described for a triangle rack.
Very much like the 8-ball 2 row break. Setup the cue ball 1 ball width (or so) off side rail, use maximum inside spin. Hit same side wing ball very near dead on (do not hit head ball). The struck ball goes straight down into the short rail, spin brings it back to your corner pocket. Opposite wing ball will bank 2 rails to diagonal foot spot corner pocket.
Cue ball comes back up the table to short rail to near corner pocket. You have a foot spot shot left for the 2.
Critical factors which require dialing in a specific table.
1) Where exactly to strike the wing ball (know cue deflection and swerve of cloth) and the short rail spin out of the wingball. This is affected by speed and rail condition.
2) Speed. The two wing balls will collude mid table at certain speeds. The key is to get the speed so they just miss each other.
Once I have a table dialed, I can pull the double off 30-35% of the time.
If one wing balls does not go in on the break it is a sitting duck and a good setup for the spot ball.