I recently got a Macintosh LC 520.  It has System 7.1 installed but it contains a whole bunch of old garbage & extensions so I wanted to do a fresh install.  However when I insert my 7.1 install disk I get an error that 7.1 is not supported on this Mac (tried several versions).  Is there a special version of 7.1 I need for it?  Can someone point me to an image?  

Thanks