What's most impressive about that build is that the AK47 design is optimized for specially-tooled mass production factories, not DIY. The AR15 is a more modular design that's easier for this sort of thing.
The AK47 receiver (which is the "gun" in the eyes of the law) is much simpler than the AR15. Its literally a piece of folded sheet metal. (I have built both in my garage from scratch)Now headspacing and barrel pressing with the AK is a bit more complicated but still there are ways around this work.