when it comes to rebuilding a thing, i think whats important to wonder is would you even build it the same way? I remember seeing an article on ars about the engines for the Saturn 5. They took over a thousand hours of weld time at a level of skill and quantity that was built up during that time period. And they got them working via experimentation. Building the now was done differently. They 3d scanned the parts and used modern additive and cnc machining and used way less welds (one can argue additive metal is just cnc welding but I digress). And then simulated it in the computer. I remember a discussion about the baffles in the nozzle to stop pulsing in the combustion, that was figured out in destructive trials of this incredibly difficult machine. You'd do that in simulation now.

I likely got details wrong.

But it's to say that part of "they don't build em like they used to" also means "they learned". Look at bridges, they don't look like Brooklyn or Eads anymore. They used to build them with waaay too much steel.

That said roman concrete is a thing they've been chasing for a while