The 60's wiring was too small anyway, especially for some of the modern devices a lot of people are using.
If you're building your own harness, or figuring loads based on wire size etc, best thing to do is calculate wire size based on load/temperature/voltage etc.
Use 12 or 14V, DC, copper conductor, no conduit at 90*C, single set of conductors. Limit voltage drop to no more than 5% at the farthest object in the circuit.
Who cares how much horsepower it has, all that matters is how fast it goes!
Untested 331, lots of suspension, chewing up corners.