What 8.25 rear axle fits my 1964 Dodge Dart best?

You can also use an 8.8 differential sourced from a mis 2000s Ford Explorer. There are threads on the forums that will detail the parts and process, it will need to be shortened of course, but is very stout, and comes with disc brakes, 5 on 4.5 bolt circle, typically a Traction Lok (Fordspeak for Sure Grip) carrier, and either a 3.73 or 4.10 gear ratio. I have no idea what availability is going to be like in the Netherlands however.