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.