My opinion if using 80% lowers you would need to get a FFL 07 as well as possibly register with the DDTC to comply with ITAR. Since 80% lowers are legally considered just chunks of steel or aluminum not a firearm receiver which you would be manufacturing. On the other hand just assembling a gun from parts should not constitute manufacture. But that is my interpretation based on what I have read, but I am only a FFL 03 and have not done extensive reading concerning manufacturing firearms.