On the 70 and E-Bodies there is a lap belt and shoulder belt that buckled separately and they were colored to match the interior until the last part of production 1971 when they all became black. In 72 to 73 E-Bodies (all black), the shoulder belt was able to attach to the seat belt. So I guess you call the 72-74 seat belts a three point belt. Others may have more information. I'm just going off memory and my experience.
Years ago when I drove Kitten (70 Challenger) off a ten foot embankment, I replaced the front seat belts with the 72-74 style. I was always told that after a major wreck, you should change your seat belts. Don't know how true that is, but it was a pretty good impact!