I think if I read the question, you are asking about converting the configuration and not the software image. I had 14 Cisco 6500 deivces that I converted from CATOS to IOS. I did not use a tool. I took the CATOS configuration, looked at it and configured the IOS device from scratch. Remember that you are already running IOS on RP, so you have that part of the configuration already. Configuring layer two ports, spanning-tree, and other layer two stuff can go pretty fast. Not sure if this is a help, but is the path that I took and it worked well for me.
