Here is how I did mine:
got my battery box mounted as well as my cutoff switch. I really didn't want a switch on the outside of the car all of the time. So I ordered the Moroso 4-post cutoff switch along with the push/pull handle setup.
I grabbed an extra passenger's side taillight and drilled it for the rod to pass through. That way I can have it for the track so I can be legal. Then once I'm done I can pull the rod and the taillight and put the un-drilled taillight back on. That way I don't have to worry about someone jacking with it. I can still use the switch as well, and it will be locked securely in the trunk.
I mounted the switch on a piece of angled aluminum and mounted it to the side of the battery box, with another piece of metal on the inside of the box for reinforcement. Used all 1/0 welding cable, copper lugs that are soldered and crimped, then finished them off with adhesive lined heat shrink tubing. A little time consuming, but the finished product is well worth it and gives me the security of knowing it wasn't thrown together.
Ran the following cables:
Short lead from positive battery post (marine terminal) to cutoff switch
Long positive run from other side of switch all the way to the starter(through the inside of the car)
Cable from post on starter to lug mounted behind fender for accessories
Long negative run from negative battery terminal to bolt on K-member (through the inside of the car)
Short negative cable from battery post through trunk floor to frame rail
Long positive run (8 gauge) from alternator to battery