stock rear will hold up with some 31 spline axles, stock rear with just 4.10s and a drag radial i wouldnt leave harder then 3,500. Put some moser 31s and a truetrac in it and launch as hard as you want. Input shafts my friends had bad luck, he went through 3 input shafts before going to a tko 600. He was just a bolt on car on a drag radial. Last time he broke it was shifting into 3rd gear. I have no idea how he broke it so many times