I have number 1 running from the trunk to the starter relay. Step it down to 4 gauge from the relay to the starter as it is only <12" or so and leading into the headers.

Number 2 from driver's side 7/16" boss on block below the heads to frame rail. Number 2 from pass side 3/8" boss on block below head to other frame rail.

Number 1 grounded to body/remote relay in the trunk. Number 1 from negative side of battery to frame rail.

Can't say everything is tested, but just make sure you have a current return path at least equal to the positive supply and all points/connections clean, clean, clean. I purchased some conductive grease to keep corrosion under control.