Those are the files you need to make vial work on your Bastard Keyboard.
- download vial: https://get.vial.today/
- flash the hex file found in the release section that matches your keyboard
- sideload the json in vial and configure your keyboard !
If you want to modify the firmware, you can fork vial's QMK fork, and copy the bastardkb folder inside the keyboards folder from the fork.
Then, modify the layouts or other options, compile with the appropriate command, and flash. You can find more info in the bastardkb qmk folders.