The Rebbe clarifies that righteous non-Jews have souls from the good in Kelipat Noga, not from complete impurity, and cites sources on converts. He advises that if one has an older brother, he should request full permission before pursuing a match. He concludes with encouragement to maintain daily study in Chumash, Tehillim, and Tanya.
https://www.torahrecordings.com/rebbe/igroskodesh/015/010/5492