each shank might be 4 inches thick?
If this was urgent yesterday and you made the dish, please tell us how it worked out.
If faced with this dilemma, and I had time, I'd go back to the butcher.
If not enough time, I'd cook the beef shanks longer than planned (use more liquid, as need), to make them falling-off-the-bone tender. Then serve the deboned meat and bones separately, for guests to eat as they wish.