For sale is a like new Magpul SL handguard in carbine length. It has everything you need to outfit an OEM carbine upper: Impact QD sling mount with rotation limiter, and Impact Mount-N-Slot Surefire Scout mount (reversible). I mounted it on a Colt 6933 upper shortly before selling it, and it was snug and tight.
About $100 invested in this setup, yours for $55 shipped.