Can Sino-Soviet immigrants go through the immigration formalities between China and the former Soviet Union in the 1960s and 1970s?

You can go through the immigration formalities. In the 1960s, during the honeymoon period between China and the Soviet Union, there were many exchanges between the two countries, which only existed at the diplomatic and official levels. There are also many personnel exchanges between the two countries (especially in the border areas), and intermarriage is more common, so immigration due to marriage occurs from time to time in the border areas. However, with the bad relations between China and the Soviet Union in the 1970s, this situation basically stopped.