So you say your in good shape now, but want to be better? You've got what 6 months? thats more than enough time for 1 bout... especially 3 1 minutes... if its 1 minute just do loads of Anaerobic fitness drills so you can blast away as hard as you can for the full 60 seconds... shouldn't be hard to get in shape enough for that.

just do what ever you can do to train with some one who knows and is experienced in technique... thats whats gonna be important... 3 1 minute rounds will be a walk in the park if you do sprint and punch out drills for even a few weeks.