If you go to the John Deere web sight then go the there parts look up and type in 520 under model then look down the list.The 520 snowblower does come up and it gives a parts break down.I gave it a try to make sure it worked and it does.I think that model was made by Ariens or Simplicity?

I went to the site. I could see the drive belt and some engine parts. I was looking for the guard and rubber blade flaps.
Any idea what the Ariens od Simplicity cross would be?

Try finding what you need from the Alphabitical list this is from the Online part catalogue page.

Here is a link that might be useful: Online catalogue page