Alternator wiring

You say you are using the regulator that "looks like the original black box". That's a little bit ambiguous; the original '60-'69 regulators were a black box with one "IGN" terminal on the right side and one "FLD" connection on the left side, and the original '70-up electronic regulators were a black box with white or yellow ink stamp ("Chrysler electronic voltage regulator 3438 150" etc) and a single triangular rubber-booted 2-wire connection on the front of the box. Nowtimes, there are several different electronic replacements for the '60-'69 style regulator that fit, hook up, and more-or-less look like the original '60-'69 units. Which exact type of regulator do you have? I am guessing that you mean you have an electronic version of the '60-'69 regulator. In that case, you ground one of the squareback alternator's two field terminals -- it does not matter which -- and connect the car's one and only field wire to the alternator's other, non-grounded field terminal.

Green1 is correct, you cannot just toss a big-amp alternator into an early car without risking extensive and expensive damage. See here and follow the links it contains.