I would go with 2/0 weld cable and run both the pos and the neg cables for the lenth of the car up to the starter motor and the motor's ataching bolt for the ground.
I use 1/0 weld cable when the battery is in the front just for grins, relayed glow plug single runs (one wire for each glow plug via a relay and fuse, #8 wire), real load reduction relay (nothing but starter wire and glow plugs get power), but then I am just a bit crazy! :twisted: