620 Aluminum Disc Brake Upgrade Kit (only for drum (pre-'78) trucks) $450
This is, basically, the same kit as the 320/520/521 kit, but with different inner bearing adapters and metric hardware.
Kit allows later model hubs/rotors/calipers to mount onto the stock kingpin suspension with a simple modification to the spindle. This kit uses '87 D21 rotors, not 720 rotors as the previous kit did. Hubs from multiple years of Nissan trucks can be used, but some may require modification to clear the center holes of your rims.
This is the aluminum version of the previous steel kit, and does NOT require the wheel spacer to fit stock 14" steel rims.
Installed pics courtesy of Eric Capps. Thank you!