As discussed via phone ,stud bolt for cover of V-4770 are size ½” x 2 ½” grade L7 (low temp) total require = 12 ea per unit. Pailin store have available size ½”x 2 1/2'” grade B7.
I think stud at cover we can re-useable or replace with grade B7 as we have , However the nipples above the cover may be broken while removal ,Please see more detail as picture below krub.