I installed a guntech usa 2 piece quad rail a couple of weeks ago, took three of us to get it installed, but that was without a delta ring tool. It didn't require any any filing or anything to get it to fit other than brute force as it compresses the delta ring all the way, so I'm not sure if it's ever coming off. I picked up the 7" carbine one as I didn't want to deal with removing the front sight and the gas block. It's a really good fit and has no movement once we got it mounted and out to the range.
I've also heard good things about the Ultimate Arms Gear quad rail but I wasn't able to find one in Canada, I lucked out and got my guntech from a Canadian eBay seller.