hughes rockers

want to get the hughes shaft mounted rockers for the 360 magnum engine I am doing for my son's duster, I am running rhs indy x heads, rocker bolt mounting holes are 5/16, is this what the hughes kit comes with? didn't see anywhere that it say's the size, if so how much spring pressure is to much for a 5/16 bolt? hughes say's currently out of stock, is there anywhere else to get these rockers or is there another brand that works good, will be running right around 550 lift cam.