Way back ... like 1969 ... we ran a 1957 2 door tradesman wagon in E/Modified Production. We kept breaking the stock axles. On the advice from a Car Craft magazine (I think) article we swapped in dodge axles. As I recall all we had to do was shorten them a little. For the life of me I can't remember what these axels were out of. Does anyone out there remember?
You probably pulled the axles out of a Mopar 8.75 rear. They came in a number of different cars, and are hard to find these days. because Mopar had too may different rears. I worked at a speed shop in N.Y. back in the late '60's/early '70's. Every Monday morning the owner had a standing order with the local Chevy dealer, and a truck would arrive and unload about a dozen Chevy axles for all the guys that broke them at the track Sunday. I still laugh about that! We ran an 8.75, the very same 8.75 in our hemi Super Stocker, then put it in our Pro Stocker, from 1965 until 1974, and never even looked in it. Big Daddy Don Garlits ran 8.75's in his fuelers up into the rear engine era. They are every bit as tough as a 9 inch Ford, but require less H.P. to turn due to a more effecient design. There were just many more 9 inch Ford's made than most any other rear, that's how they became so popular.
You might want to contact Aubrey Bruneau at BruneauPerformance.Ca (a Canadian site). He makes the setup, BUT, the tri-five rears wont work; it has to be the 58-64 rears. Butch/56sedandelivery.