I am planning on building a new "all-around" AR so of course I got out the Brownells Bible.  I just buy complete uppers and do the lowers myself.  Anyway, on pg 1 they have the DPMS uppers with the stainless bull barrels.  My question is does anyone know what gas block comes on them i.e. does it have rails to mount a flip of front sight or not.  And if it does not have rails how hard is it to replace it with one that does.  Sorry for the long post.  Thanks in advance.

 Thats the set up I have for my patrol rifle.  The bull barrel upper comes with a plain block.  Brownells does sell the bull block that is a 4 rail block.  It is easy to replace...... I then used the flip up front site on it for my set-up.  Good luck.... it is a great shooting upper.