This you may have to contact Kubota customer service or a dealer because there may not be many people in possession of a 520 for quite some time. Most dealers are saying they can't even get one yet.
Good luck, hope you find your answer.
Just got my new 520 with the plow option. The part# is V4308B on my build sheet. The part# in the 500 brochure is V4308A, so not sure if there is a difference between the two. Hopefully this will help you out if you have access to a dealer. On a side note I am super happy with the quality of everything and the dealer I bought it from. Awesome machine!