The lower will fit a real upper but it would require shims and someone who understand blueprints to be able to fit the fire control group. Someone with those skills could much more easily complete an "80%" lower. Correct me if im wrong but the high pressures reside in the upper and the quality of materials in construction of the lower are not as critical. I'm merely speaking in terms of being able to fire without blowing up in your face not reliability. They did build really nice replicas that happen to fire plastic BBs... The ATF is embarrassed as usual because they are clueless. It could be converted but it wouldn't be an ideal platform to build on and there are better ways to build an AR that require much less hassle and would result in a much higher quality end product. The company that makes these admits this. The only part that could be converted is the lower. But it simply is not worth it and is not easily done...