I don't know, but as a kid I enjoyed the hell out of tearing stuff apart and putting it back together. However, I'd rather buy an ar lower already put together. Same goes for the upper. Although, to get exactly what you want, you usually always have to take stuff off and replace with what you want. Luckily ars are easy to disassemble and reassemble. When I run across one that is put together just the way I want it, it's hard to pass up. I have my eye on a LWRC with ambi controls, that fits that description to a tee...
