It is not simply a matter of having schematics and production plans. You need the right kind of factories and, as you said, production lines. Those don’t exist anymore. You have to retool and rebuild everything.

Far cheaper to start from scratch, as SpaceX has done, using the knowledge gained in the past combined with the technology and engineering of the present, to make something new and cutting edge.

Thanks for the update, Bob. One would think NASA would have kept copies of all schematics and production plans given that they paid a vast sum to these companies. Oh well…

Those Saturn 5 production lines don’t exist any more. They were shut down in the mid-1970s and are long gone, with many of the individuals who worked on them long retired or even deceased. In addition, the companies that built the Saturn 5 are also long gone.

Moreover, the technology has changed. NASA tried to resurrect the J2 upper stage Saturn 5 engine for SLS and after spending billions on it mothballed it because they found it to be “overpowered.”