Rear end advice for racing with a 4 speed

One small point. Disregarding the other parts of the strength equation.....a Ford stock 31 axle is about 25% stronger than the 28s.
A 35 spline axle is almost 50% stronger than a 30 spline.
And a chromemoly axle of the same spline is about 40% stronger than a stock material axle.
So, just the axles, good 35 spline axles are at least 100% or more stronger than stock 30s
35s are available in good material for an 8 3/4, but I believe ONLY for a spool. (Unless dapco offers side gears for their locker)