the Vltor VIS is going to give the LMT MRP a run for the money as a monolithic upper alternative, if a free float one-piece upper floats your boat. uninterrupted top rail, in carbine, mid-length and rifle lengths. takes standard M4/16 type barrels. the bottom rail is removable, unlike the MRP. it's nice - eric at Vltor's a good designer.
http://www.vltor.com/vis.html