If you are running a one-wire alternator you don't need the old regulator.
If you are using the regulator as a junction and only using the B post, I don't think it will cause any problems. If you study the wiring diagram for an AD truck you'll see that a wire runs from the B post to the amp guage.
I'm not a big fan of the MAD Electrical guy. I feel his solutions are geared to selling his products, and that often there are better and cheaper ways to solve a problem. He's not evil, or even wrong, he just annoys me.
I stopped reading the article Cletis referenced at the point the guy asserts he has no vested interest in the answer because he doesn't sell alternators. I already knew he sells a kit to wire an alternator, and I'm sure his discussion points you toward buying his 3-wire kit.
While I'm not a fan of the MAD Electrical guy, I do agree with his conclusion that you are better off using a 3-wire approach. The 1-wire approach requires that you rev your motor in order to get the alternator to start charging. Not the biggest problem you might have, but not the best way to get the job done.
I think the best approach to getting the alternator going is the charge light approach. The diode approach leads to overcharging the battery, which can reduce battery life.
