What 8.25 rear axle fits my 1964 Dodge Dart best?

Yes, i see now that you're right. I jumped to conclusions too fast.
It appears you're in another country though. So, all bets are off, unless you've found that our information is the same as yours. That's not always the case. As an example, slant six engines were made up until about 2000 in some countries. Here, the last year was about 1987. So who knows? It worth doing some research on for sure. If you find an 8 1/4, just know they are pretty tough rear ends ans can probably take most anything you can throw at it as far as a street car goes.