I wish I could say it was Rarity, but not just yet! However, Hold onto her, and keep it in good shape, and it will become quite a nice peice to have.
I would already classify an origional Super 600 with a G3 as collectable.
Please let us know how you go when you get the time to go over the carby on this one, if you get stuck, let me know, I am happy to swap a fully restored carby for your current one if needs be.