Have a look at the Aero Precision handguards. Believe me, they look better in person than they do in pics. Quite light and really high quality. It comes with shims. Many say they didn't have to use shims, but I uniformed a receiver and needed to use all the shims.
I really love that handguard. I have one of the Seekins Precision BAR quad rails and it's my favorite quad rail. A buddy of mine got the Spike's version and it has a lot more machining detail similar to yours.