Here is the place to go for the guide, you might want to save it as a text document and read it because you will have to scroll a lot if you view it in the web page.
It's on
gamefaqs.com, all you have to do is search for Metal Gear Solid 2 and click on 'FAQs' and then look for the guide that has 'Big Boss rank" in the title.(I checked it out while writing this and I'll have to wait to get you the exact page if you would like me to.)