Has anyone built one with a parts kit and one of those receiver flats on the market? Back in the late 90's I built a FA 91 from a G3 kit and a receiver from federal arms. Still shoot it and works great but there was a down side, the aluminum receiver does not support the cocking tube so you loose the free floated barrel (wtf). I keep seeing the receiver flats for sale and wonder if it would be an easy swap. So what do you guys think?