What size drums are on my 89 GT

I installed my rear drum brakes 3 weeks ago but it seems now that I need a spring kit because shoe hold down springs came loose. I went to Kragen Auto and they asked me what size drums I had on my 89 GT 5.0, 9", 10" or 11" inch. Now im kind of confused. Did for put all these 3 options to choose from or what size of drums do I have? When I asked for my brake shoes I wasnt asked what size I had they just gave me the shoes and they fit perfectly. Thanks in advance.
 
Yeah that's what i thought but he kept insisting on a size. He asked me to take all 3 sets and if the others didnt fit to return them. I said that I didnt wanna make 2 trips. I thought all of that shouldve been taken care of in their database. I think he was just giving a mustang owner a hard time...he kinda had an attitude.