Chestnut shank on a contrasting wood makes a very good looking market crook ,Chestnut is a favourite of mine and the bark gives the shank a lot of protection naturally a few coats of oil and it will look great.I havnt had any need to straighten chestnut as of yet they do grow straight like hazel.
they come close to the looks of rams and buffalo horn in looks..
I would advise you to out a hardwood dowel across the top of a crook it will give it more strengh.