I know everyone says Loughran only had a left, but his youtube clips show him scoring quite a bit with his right. It didn't seem to have power, but he uses it a normal amount of time.
As you mentioned, Ingo and Coetzee were very much right-hand orientated boxers. One less well-known example would be Ralf Rocchigiani, brother of Graciano. Although he had a brilliant left jab, he never seemed to throw more than ten jabs a round. He also had a very weak left hook which he almost never threw and seemed to get into trouble when he did. Ralf did have an excellent straight right hand, which was best thrown as a counter-punch. He could also cause a lot of damage by banging away with it on the inside. He beat Carl Thompson for the vacant WBO title when Carl had to retire with a terrible shoulder injury (that was leaving him open to right hands); he seemed to be champion for quite a lot time. He fought a very careful style and had ridiculous heart, so while he was hurt and dropped quite a few times, he was never stopped despite fighting a lot of huge punchers. On the other hand, despite his power, he rarely scored stoppages because of his cautious style, thus not breaking the trend of German boxers being skilled but unable to finish their opponents off.