If you change hy draulic lifters to roller rockers do you need longer studs on a big block 396..the old crow feet style rockers set lower it seems and there is more thred then that

the lifters have nothing to do with the rocker arms.
as for the rocker arm studs, no, you shouldn't' need to change them- and i've never heard of longer than stock rocker arm studs. like any other fastener, as long as you've got as much thread sticking into the nut as the diameter of the stud- in your case, as long as you've got 7/16" of thread engagement on your 7/16" stud- then you are good.
the fun part comes when you realize that your stock valve covers will no longer fit over the poly lock nuts that hold the rocker arms down and you need to try to find a taller valve cover that clears things like the brake booster and heater box.

thank you we already have the new value covers that will fit...now we just need to get the rockers ajusted...Thanks superrag

i ilke to say thanks all we got the job done and the studs did have to be replaced to give us the thread we needed. now off to timing