To be 100% honest, you just can't get better at running without running. Training adaptations are very specific. You can improve your ability to breath, but then as soon as your start running your breathing will be fine, but your legs will feel like sludge because they haven't gotten the muscular endurance adaptations to get better at running. Honestly at 20% bodyfat I would consider trying to maintain as much muscle as possible while shedding a little bodyfat. That will help a lot with running performance.