I just received my new DPMS 308 LR 18" the other day.  I ordered the factory railed hand guards, which as I understand is made by YHM.  I was wondering if there is an after market FF rail (SWS, DD, Etc.) that would fit over the standard gas block.  It seems like that would be easier than replacing the rail and the gas block.  I would like a rail that covers all but the last 2" or so of the barrel.  As it stands now the rail extends to, but does not cover any part of the gas block.  My reasons are two fold: I would like to mount a bipod closer to the muzzle, have more options for light placement, and I think it just looks better with the longest rail system possible.  I would prefer to keep it around $300.  Thanks.