Best disk brake kit for 65 Dart?

The "best kit" might be the factory 1964-72 Kelsey-Hayes front disks, which were also used on Mustangs, but very rare. I doubt you can find 1973+ front disks in "any junkyard" today, as memike said. It is rare to find any pre-1980 Mopar car around northern CA today and most are quickly stripped in a few days. But, you can buy the 1973+ kit new for ~$500 from many sellers. Wilwood is ~$750, then you are locked to them for expensive spare parts. Rear disks are mainly for show. You may find you need to change your rear-end to handle a beefed-up engine. If so, some people use a Ford Explorer 8.8 rear (cut down), which gives your rear disks gratis.