The shackles are only a pivot. With the spring on top of the axle, the spring perch is the weakest link.... With the spring behind, I'd say the constant flex and pressure on the batwings and the spring perch bolt makes them the weak link. Guess I've never seen a shackle break, but I have seen spring perch's break. Doesn't matter which gives first, with the spring on top the components and hardware are much less likely to fail.

I don't build anything with a straight axle anymore, IFS is so much better handling. Never have been one to go in for "the look" or the most current fad in suspension. My preference is always to the best performing suspension for the money spent. I place value at a higher level then cost...... I don't use old axles or spindles because of the "unknowns" in their past life....how bad were they abused, overloaded, or neglected????? Magnafluxing will show cracks, but how much misuse and abuse has there been on a 50 or 60 year old axle? Another thing, all those pieces from the 30's and 40's were designed for 30 to 40 mph cars with skinny little tires. How much does a big horse V-8 and sticky radial tires exceed the design limits of the components???? I'm not some kind of scardy cat, but I feel there's enough inherent risks in driving a high performance car in among today's low performance driver's that I choose to not take any extra risks by using old, worn out parts at a level they were never designed to perform at........