But, but... we'd certainly go back (with 1960's tech), but we lost... the.... tech. Sorry, can't find it. Sorry, can't recreate it.
Three words come to mind, I think it likely you and I are familiar with: Van Allen Belts.
We haven't "lost the tech". We have original equipment sitting in museums. But why would you even want to recreate a 1960's spacecraft? And we were putting men in orbit in the early-to-mid 1960's; it's much easier than going to the moon.
Just because McDonnell-Douglas could build Gemini in 1964 and get to work (most of the time) and North American Rockwell could build Apollo in 1967+ and (eventually) get to work really well, it doesn't follow that Boeing can build Starliner in 2024 and get it to work well on its third flight (first crewed flight).
Engineering doesn't work that way. Just because someone did it well 30 years ago doesn't mean anyone can do it well today.
And if the "anyone" institutionalizes enough bean-counters in senior positions, who don't value or understand engineering and think of engineers as interchangeable cost-centers, well, they're that much further from doing it well today.