The Dana 60 in my Cuda has dual Mark Williams steel caps and 40 spline M.W. aluminum spool and axles, it had a set of Pro 5.86 gears in it when I bought and a LPW aluminum cover with the load bolts in it as a roller. I changed the gears and spool to a set of 4.56 with a Strange Engr. steel spool up This car has reportily ran 7.60 at 184+ MPH weighing 2500 lbs with the driver and a KB aluminum B1 motor with a blower running methanol, all the rear end parts look excellent
I figure that no one would make or sell aluminum caps for a rear end in anything other than sport car or extreme high speed racing where there is very little shock to the drive train confused

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)