Mine is that same slickside upper and the lack of a dust cover and shell deflector has not been a problem at all. The rail IS taller than any forearm on the market, but if all your going to run is optics that's really a non-issue too. As for the lack of a forward assist, those things are worthless IMO. I put a plug in my 300 BLK upper and will do the same with every build from now on. I'm not wasting any money on them any more, in the 30+ years I've been shooting these rifles a forward assist has NEVER solved any problem and has actually created a couple for me.