This is a very loaded question, but I'll give some economic indicators on what the situation in Korea was in the early 1960s. Tens of thousands of Korean living in Japan did immigrate to North Korea after the war. They had few civil rights and social acceptance within Japan. Additionally, neither state of the Korean peninsula looked that dissimilar from the other in the 1960s. Both were widely considered to be illiberal and autocratic states that were quite poor and heavily backed and influenced (if not puppeted outright) by the competing superpowers.

For South Korean citizens, I can attempt to speculate and shed some light based on the economic and political situation of the time.

GDP per capita was very similar between North and South Korea ($1100-1300) for the first half of the 1960s. They largely grew apace, and North Korean per capita GDP overtook the South for some time in the early 1970s.

In that time, South Korea was certainly the more politically unstable place of the two. The dictatorship of Rhee Syngman had been overthrown in 1960, being replaced by a more liberal Second Republic. The Korean Won was rapidly inflating and losing value however, and prices on basic goods rose, and unemployment was high. The Second Republic proved politically unstable, and was quickly overthrown after just a year in a coup orchestrated by conservative factions in the army, putting an authoritarian junta in control. Park Chung-hee would come to power as a military dictator, and South Korea would remain a military dictatorship under various iterations for the next 25 years.

South Korea's regime began to reign in economically liberal policy and instead began to institute a greater role for the state in economic development, and began a series of 5 Year Plans in 1962. South Korea embarked on a programme that is called Import Substitution Industrialisation by developmental economists. Protectionist policies were put in place, state investment into research and development projects for new technologies was introduced, steep import tariffs on foreign goods put in place, export revenues greatly increased, and state-owned industries began to take much precedence. The best known example of these is POSCO, the state-owned steel manufacturer that was established in the latter half of the decade and still exists today.

The 5 Year Plan programme increased South Korean GDP immensely, with the 1986 GDP being over 10x higher than the 1956 GDP. South Korean per capita income greatly increased during this time, and began to depart away from that of North Korea significantly in the latter half of the 1970s. The contrast got its current stark character during the 1990s, when mass-flooding hit North Korea and triggered an economic and social collapse that it has only recently begun to make any significant recovery from.

With this being said, it could be possible to assume that sentiment and willingness to immigrate North for South Koreans may have been at a height during the 1960s and 1970s, and likely steeply fell off by 1980 as the economic situation for average South Korean worker began to improve tangibly.

This is however, very hard to say beyond the realm of speculation. Historians generally don't prescribe ideas such as this, and it was administratively difficult and nearly impossible for a South Korean to leave the country for North Korea. In the 1960s and 70s, it was incredibly difficult for South Koreans to leave the ROK for any reason at all. Additionally, the military dictatorship took a harsh stance against any movement or individuals that could be deemed 'pro-North'. South Koreans would have been unlikely to say anything positive or envious on the North in the public sphere, and certainly would not talk about defection, as this could be (and often was) used as a reasoning for arrest and torture by the regime.

If you're interested in learning more about the economic policy of South Korea during this time, I'd recommend Bad Samaritans by Korean economist Ha-Joon Chang.