To the best of my knowledge, 922r rules applies to firearms BEFORE importation into the USA or DURING domestic manufacturing and/or the conversions of imported "sporting" types of firearms into what the ATF calls "non-sporting" firearms. The "end user," the purchaser/owner can put any other parts onto his/her own firearm without violating U.S. Law, specifically 922r.
That's my understanding, so if I "was" going to manufacture a firearm, I would used the easiest U.S. Made parts to swap out later, like a U.S. Made magazine, handguard, buttstock, pistol grip and charging handle... Once the firearm was fully completed, swap out any of those parts for parts I really wanted.
I know many want to play it safe, which I don't blame anybody for doing since I would do the same. Plus, nobody wants to deal with some dick-headed "Barney Fife" from some small town Sheriff's office, questioning the legality of your firearm(s) since in his limited mind, he knows all the ins and outs of every law within the United States, when in fact, he most likely barely knows his own State laws... Even worse, a "Range Master" with a god complex, who "claims" to have a buddy that's an agent with the ATF, FBI, CIA, DHS, NSA and so on, as he writes down your vehicle's license plate on his spiffy little note pad.
On a serious note, I cannot ever see a local U.S. Attorney's Office ever taking on a simple 922r violation case and presenting to a federal grand jury for prosecution... Unless there was some "other stuff" that you're doing, causing them, the government, to REALLY want you at any cost. I don't even think an ATF agent would even present a case involving just a 922r violation to the AUSA's office, unless there was something more serious to go with it, like somebody manufacturing a fully automatic firearm or several unregistered SBRs and/or being involved in some other serious criminal activities.
Would I ever test this? Probably not. I'm simply throwing this out there for a thought. And by no means am I an attorney, acting like an attorney or giving out any 100% factual information... Yes, this is my disclaimer!!