My 74 Pantera appears to have a 3 guage battery cable between the starter relay and the starter, which seems a bit oversized. Is this the correct size?
Just like mine 74...
If anything for the cable length front to rear and amperage of a typical starter motor (115A) 3 gauge is a bit light.
IMHO, if the battery is far away from the starter, the bigger the better! And use braided copper, not solid wire. On one of mine, I used 0-gauge arc welding cable to reduce the voltage drop.