I'm quite surprised this hasn't been done yet.
Madara's plan succeeds and he takes over the world. Naruto is sent back in time to defeat him (a wizard did it), arriving at the point a little before the final Madara/Hashirama fight.
This is BM Naruto vs EMS Madara. There is no time limit for Naruto, and Madara CANNOT control/interfere with the Kyuubi in any way.
Both have standard equipment.
The battle takes place on a clear, even plain, with both starting 50ft away from each other.
Can Naruto save the future?