Hi Grand dog, I can't get the .pdf to work, so I don't know what your filter looks like. The 520sp is listed as using only the Walbro carb, and this saw has the Tillotson, some of them had the Walbro. I don't know if that would affect the filter that was used.
I don't have the saw right now. It is on the way. The guy I got it from on ebay said it would only run with the choke pulled out. I asked him to pull the cover and see what kind of carb it used before he shipped it, so I could go ahead and order a kit. After pulling the cover, he decided to pull the top off the carb. He said it had a lot of tiny rubber chunks in it. He cleaned it out, put it back together, and the saw started up and ran great. He said it looked as clean as a new saw, hardly used, but will need a new air filter and fuel line. As soon as the saw arrives, I'll look at the filter. Maybe I can send you an image of it to compare with what you have.