I put a Yankee Hill Diamond quad rail on mine and my boys carbine. His has the regular A-Frame front sight and I have the Yankee Hill folding front sight. No problems with either rig.
I also had the Hogue FF overmolded tube with a standard gas block, no rail on a 20" 204 upper, didn't have any problems with it either.
You'll have to give a better explanation than "not fitting right".
