Many groceries will be tied on 4/0, 5/0, or 6/0 hooks. Don't be shy use big hooks. To tie this type of big fly and make it ride correctly you need the large hook to act a keel to orient the fly. The flies will usually end up between 5 and 10" long (in reality, most will be 6 to 8"). To make this size fly proportional and still have the point of the hook exposed, a hook with a large gap is required. I have found that large flies with the hook point buried in material on the underside of the fly do not hook up very well.
As far as shank length goes, organization and practice are the keys. Look at Bill Catherwood's striper flies and you will note that he choses 3/0 to 6/0 short shanked hooks on some very big flies.
Try moving up to a 4/0 and plan to finish the fly with 1/8" of extra room at the eye. You will probably find that you won't have the extra 1/8" at the end but you will be able to finish off the head nicely and keep the hook point far enough forward to remain exposed.
I seem to fish grocery flies about 75% of the time. They take effort to tie, patience to cast, but your rewards are likely be some very big stripers.