I didn't see any other threads for this, so I thought I'd post one. Does anyone know who, if any, makes a 7.62x39 upper assembly with a 20" barrel? I have been doing some searches and I can't seem to find any info out there. And, if I choose to build an upper, can I use a standard AR-15 upper, and just get the 7.62x39 BCG, barrel, and magazine, or is there a specific 7.62 upper that I need to get? Any help is greatly appreciated.