Kurt Zisa isn't too hard to beat at around level 70. You might want to fight the Hades Cup at Olympus Coliseum. After you beat it once, you can try to beat it with Sora alone to get Donald's most powerful weapon, then try the Timed Battles to win Goofy's most powerful weapon. By then you'll surely be strong enough to win.
Give Goofy and Donald all the Mega-Potions they can carry and set them on Conservative, otherwise they'll waste them before you're halfway through the battle. Try to cast Aero on yourself before Kurt uses the magic block, then lock on to one of its hands and keep attacking. Hit triangle when you're locked on and Goofy or Donald will attack the target.
Once you've destroyed the magic block, Kurt will be stunned for a while so you can clobber his little wormy head.
Kurt creates a globe of protection and starts flying around. Use magic. Gravity does good damage to him when he's shielded. It takes a lot of MP to destroy the shield, so maybe wait until Goofy learns MP Gift and make sure he has that ability set before the fight. After you destroy the shield try to cast Aero before he uses his magic block again.
Kurt also does some spinning attacks once in a while. You can jump over his horizontal spin and use Dodge Roll to avoid his vertical spin, but i usually just hide in one of the valleys of sand or get hit.

G'luck!

You think Kurt's tough, wait until you go to Neverland again. Find Tinkerbell in the Cabin and put Peter in your group, then talk to Tink to go to the Clock Tower. Save first.