You should read The Lords of Creation series by S. M. Stirling. The Sky People is about a habitable jungle Venus, In the Courts of the Crimson Kings is about a habitable desert-highlands Mars. The POD would actually be before the 1960s, such as when microwave tests are used to determine if oxygen is present on Mars or Venus. By the 1930s and 1940s there will be a few scientific divergences, and the scientific community and perhaps science fiction community will be in a better place regarding hypothetical habitable neighbors. Stirling conjectured that with these early discoveries, right after WW2 the US and USSR get started building rockets with the goal of getting to these other planets to see if the presence of oxygen means that there is life. Both sides don't waste a decade or so muddling around with various technologies and getting nothing substantial done. First satellite launched by 1950, first interplanetary probes, atmospheric or otherwise, observe Venus and Mars in the early 1960s. When life is discovered, that gives both sides a major motivation to get people there, and before you know it there's a moon landing, a moon base shortly thereafter, the construction of space stations, nuclear rockets, etc. etc.