So it seems it was already fairly easy and legal to build and own a very high-quality firearm with general attention-grabbing features mentioned in the article? Not a legal advice or suggesting you should do so:

1. CNC the Remington 700 action: https://www.practicalmachinist.com/vb/gunsmithing/making-rem... . This is the hard part and would probably need a week of dedicated work...

2. Buy barrel, trigger and stock.

3. Everything mostly just fits into the action, so assembly is just like putting lego pieces together.