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:
I've purchased unregulated 80% lower receivers (they're only legally "a gun" if more than 80% of the machining work is complete. At or below 80%, they're just considered a chunk of metal.) and machined them using nothing more than a woodworking router, a hand drill, a jig, and a vise in about 30-45 minutes.
The jig is the most expensive part, costing about $160 or so, but once you have it there's no wear parts and you can use the jig to build as many as you want.
You can still sell it. You just can't be producing guns for sale. There are limits to how many you can sell and when you can sell them, beyond which the federal government will presume that you are producing the guns for sale.
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.