They are easier to build due to the huge aftermarket, have more gear ratio selections (from 2.40 to 6.50), and all sorts of aftermarket parts. That's it. Note that many "Ford" 9" axles under race cars have ZERO Ford parts! (Just like a drag "Powerglide" uses no factory parts.)
For an A-body, I would rather have an 8.25" Chrysler than a 9".
