Depends on the age, but Fiberspars were the choice of masts for Gaastras under Barry Spanier. This means they tended towards being harder top. They would probably work with Mauisails, Gaastra, Severne etc. Would be worth trying if you can test rig the sail on your mast.
A new 520 mast probably wont cost you $1500, but anyway buying new means you do get a warranty if it does break.