No need to buy the new headset. But you can if you want to use the "right" crown race for your fork. It should work with the rest of your purple headset, no need to powder coat the black parts.

If you want to use the 26.4 crown race just file down the fork until it fits. I've done this before. It takes some care and you don't want to go too far. You also want to make sure you keep it relatively round. But it's not too hard.