The foundry is going to ask you if that is the final sized part or not, otherwise you are going to have to build that part up with bondo and sand it to get the mold the right size because it is going to shrink.
Also, you have to have the proper draft angle and venting to even do a sand casting of that part..which makes you have to pour the part differently and make the mold differently as well.
Been there and done that one, it was a heck of a learning process to figure out which is the best route to go about something without beating up tooling on machines to make it a finished part.