If you just want to use recalbox with the composite output, here is my file /boot/config.txt:
# uncomment if you get no picture on HDMI for a default "safe" mode
#hdmi_safe=1
disable_overscan=0
# uncomment to force a specific HDMI mode (this will force VGA)
#hdmi_group=1
#hdmi_mode=1
# comment to get jack audio
#hdmi_drive=2
#config_hdmi_boost=0
#hdmi_force_hotplug=0
# uncomment to ignore hdmi plug
hdmi_ignore_hotplug=1
# uncomment for composite PAL
sdtv_mode=2
# Overclock
gpu_mem=512
avoid_safe_mode=1
kernel=zImage
# NOOBS Auto-generated Settings:
#hdmi_force_hotplug=1
#config_hdmi_boost=4
#overscan_left=24
#overscan_right=24
#overscan_top=16
#overscan_bottom=16
disable_overscan=0
overscan_scale=1
You have to comment some lines (with hdmi mention).