Piston Question
 

So I pulled my heads off and the oil pan down. I am really only a few steps away from a almost full over haul. I haven't pulled the pistons out yet for fear of a bad ring. It ran fine before I pulled it into the garage. I was browsing Ebay and saw a auction for 305 piston rings. So of course I know they are rear so I bought them. I am new to this type of work and I am pretty sure I bought the wrong ones. Any help would be appreciated. Here is the info (NORS Muskegon #CR6007 Standard size Chrome piston ring set GMC 305 V6)