Unless you have a money tree dont go crazy buying gen parts. The basic outside pieces make the biggest difference, so stick with them.
In my opinion,
Genuine
crystal, insert, crown
Aftermarket
Case tube, bracelet, Clark hands, a decent date wheel.
Mods
this is where you should spend your time. It makes a huge difference.
Crown guards, drill the lug holes, sink the He valve in the case a bit, remove the paint on the case back and polish the lugs to make them smaller and maybe a vintage relume.
Anything else is going to cost a fortune and you will still not be able to fool that 1-2% of the population that would pick out a stock MBW vs your modded one. All the mods in the world wont make it real and 99% of the population wont know any better, so save yourself some money and take short cuts where you can. Give up on trying to fool a WIS it's not going to happen and in your lifetime you may encounter only a handful of watch nerds in real life. Most people dont know and dont care.
IMO, the main thing is to work the case to make it look vintage. If I were to see someone wearing a NOS 1665 that would be a huge red flag to me.