Just remove all wiring, and replace with an off-the-shelf harness. Mine is a Hot Rod Wires 18-circuit harness, running off a GM one-wire 12V alternator. Obviously, all bulbs & gages will have to changed out for 12V, and the starter replaced or rewound.
I'm guessing that date is not a build, but a rebuild date. 230 OHC engines weren't manufactured in '74.