Custom aluminum CR style tank......................
Anyway, I would shy away from fiberglass tanks IMO. The 550 has a very basic frame "spine" and adapting different tanks isn't too difficult. If your bike is still together, leave the fron end on if you are trying tanks, as the clamps/bars need full travel so it might limit some configurations, especially if you run clip-ons.
I just got my aluminum tank delivered, and it was worth the cost/wait. I am not a fan of 'glass tanks on streetbikes. A stock 550 tank that has been modified can also look unique and cool too!