There are so many ways to do this. I ran fine stranded welding cable from the trunk where I had the battery and shutoff, just one cable and then grounded to the body to save running more than one cable the whole length of the car. I like the welding cable because it has good insulation and bends very easily. I ran the cable and drilled a hole as shown in the sketch
and here is the actual hole but the car is apart now

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The cable runs through a big fat grommet into, and out of the rocker and there is a p-clamp to support the cable just before the grommet at both ends. I also split some plastic irrigation hose and covered the cable inside the rocker to prevent chaffing where it is hidden. Here is where it comes out the front of the rocker.
I like this because the cable takes an easy turn and is right there where the starter is (at least with the big block).
I plan to add a large fuse in the trunk this time in addition to the shutoff.
As Greg mentioned above any movement could potentially cause wear, so make sure nothing can move and avoid running the cables over sharp corners. If a large cable shorts out make sure it is protected by a fuse that will blow before too much damage is done.