The hole in the block is a clearance hole and tapped into the mains and used with a thru bolt. There is no added advantage to using studs with a nut. IMO The PSI of the thread in the main caps are the same weather your using a bolt or a stud. To pull the mains out you would have to remove the stud anyways. Studs are used to make the thread in a aluminum part a non working thread so to speak, It's not good to continually take a bolt in and out of aluminum threads.