@Callum You can either rename DFL61_HARMATTAN_40.2012.21-3_PR_LEGACY_003-OEM1-958_ARN.bin file to main.bin AND FL61_HARMATTAN_40.2012.13-7.PRC_EMMC_PRC.bin to emmc.bin and use same commands. Please note that there are 2 commands.
first is

flasher -f -F main.bin

Following by (This is optional, only if you want to get content loaded like videos, music, maps data and few other things) which comes with new factory condition phone

flasher -f -F main.bin -F emmc.bin --flash-only=mmc