Your axles will be fine. I smoked my diff after tons of 1/4 mile passes making 414RWHP. MY axles were perfect, but I replaced them with 31 splines and a 31 spline diff when I fixed it. I then sold my stock axles for 75 each, so I recouped some money and helped out another stang owner. I would save your money and upgrade the clutch first as said. I've smoked a clutch before, not cool, when you are 25 miles from home.