Car is barely over than 16 ft. Firewall to trunk is even less. Run the cable to the fire wall and use this. Short lengths of cable on the engine side to alternator and starter. Another run on the interior side to your switch box.You can see the battery cable coming up from the right side rocker. The speedway stud is above the gas pedal. Can't quite see it in the interior shot. Done, clean, simple.
Doug
https://www.speedwaymotors.com/Bulkhead-Battery-Cable-Connector-Red,83539.html