Depends on the head, and if there is enough material around the original hole to enlarge it without breaking out of the casting or into a water jacket.
What head are you talking about?
You might try to use a bottom tap and carefully cut a couple more threads at the bottom of the hole. Might not have to as there may be enough good threads left. Measure the hole depth, gasket thickness, valve cover thickness, hex nut, lock, & flat washer thicknesses, plus anything else that may have been attached to the bolt, add it all up, and cut a piece of 1/4-20 all-thread to that length for a stud. Use 2 hex nuts jammed on one end and some blue Locktight to install it. Then set your gasket, valve cover, etc. in place. Might want to give it a trial fit before appling the locktight as it may not go together but one way. You said any suggestions.