Rear end advice for racing with a 4 speed

Looking at the photos of your damaged axle , it appears as though they don't completely engage the side gear. Having learned this lesson the hard way with a 4 speedi Super Stock Dodge Charger I can tell you a ring gear spacer or thick flange carrier should move the carrier closer to the small diameter pinion associated with low ratio gear sets. (Higher Number). Probably solve your issue without spending thousands to revamp everything!