Just bought a cheap drop in quad rail from International Shooting Supplies. I've never heard of the manufacturer before...Drummond...but for $80, it looks quite good. Tried it on the Norc that I've just sold, and it went on really easily. The front goes over the handguard cap and you use two allen screws to tension it together. It sits right behind the front sight post, so it doesn't move. The rear just goes into the delta ring like all other handguards, and is also secured by two allen screws. It even came with a complete set of rubber rail covers.
I'm going to run this for a while in the Stag that I'm building. The previous owner of my Norc had installed an immitation KAC quad rail. Install is a bit more tricky, and it looks like there was some filing involved.