Are you sure Kodi does not start or it's the TV that does not recognize the resolution kodi is set to..
Can you access your libreelec from a network?
What comes to mind is I would start libreelec on another TV via HDMI...then install VNC and connect to analog output again and change resolution from VNC..Probably there are other more technical options with sdtv_mode = 2 one of them but it's not working for you so try that..
Edit...or try to set libreelec on lowest resolution available via hdmi on another tv before you connect to your older tv