I learned a couple of years ago that the people in the sixties did in fact 3d print, but they did it via electroplating and wax. It took weeks to print a Saturn V rocket bell because they had to build up something like 5mm of material onto the outside of the bell after carving the channels into the outer surface of the inner bell and then packing them with wax.
This means that 3d-printed copper (alloy) is an amazing process and material for them. You can build the kind of structurally integrated cooling channels that the people building rockets in the 60's could only dream about, and it's not a gold-plated part that required a million labor hours to build, it's something you can just print overnight.