The firmware/boards directory contains configuration for each board this firmware supports.
For the standalone board and the module built in to rusEFI Hellen boards, f0_module is the correct target. Use the build_wideband.sh script to build and package the wideband firmware: both a bin including the bootloader, and a header file consumed by rusEFI that contains no bootloader, to be uploaded over CAN (via the aforementioned bootloader).