How has the ARAK-21 not been mentioned yet? I've got a good friend who has one, and it's really outstanding.
https://faxonfirearms.com/faxon-arak-21-7-62x39-ambi-upper-receiver-quick-ship/
https://faxonfirearms.com/faxon-arak-21-7-62x39-ambi-upper-receiver-quick-ship/