If you find this stuff interesting, pick up a book aimed at hobbyist metal lathes. Just reading a little about how you set up a tiny home version can give you a whole new level of understanding and respect for this kind of stuff. Structural components are different but in that era and even to some extent today, most precision parts were machined with two primary tools: the lathe and mill. Today both would be CNC and you'd add other modern tools but the CNC lathe is still a lathe and they work the metal in the same fundamental way.

Due to the dispersed mass production in WW2 it's probably not totally true that they wouldn't fly without a custom tooling setup (it'd be a maintenance nightmare if two examples of the same model from different plants diverged dramatically, altho of course it happened) but you can be certain that it's of critical importance.